Screw tightening apparatus

ABSTRACT

The screw tightening apparatus includes a motor, an output shaft to which a bit for screw tightening is connected so as to be rotatable integrally with the output shaft and which is axially movable, the output shaft being driven to be rotated by the motor, a spring whose one end contacts a member constituting a main body of the screw tightening apparatus, and a spring receiving member which the other end of the spring contacts and transmits a biasing force of the spring to the output shaft. The screw tightening apparatus further includes a conductive member which contacts the output shaft and the spring receiving member. This configuration enables static electricity generated on the bit to certainly flow into the main body of the apparatus (ground) via the output shaft, the conductive member, the spring receiving member, and the spring.

This application is a continuation based on International PatentApplication No. PCT/JP2006/0303913, filed on Mar. 1, 2006, which ishereby incorporated by reference herein in its entirety as if fully setforth herein.

BACKGROUND OF THE INVENTION

The present invention relates to a screw tightening apparatus thattightens a screw by motor driving.

Screw tightening apparatuses include one in which a motor serving as adriving source and a bit engaging with a recess of a screw are offset intheir radial direction (for example, refer to Japanese Patent Laid-OpenNo. 2003-25164). In many cases, such a so-called offset-type screwtightening apparatus is used in, for example, a case in which aplurality of screw tightening apparatuses are disposed so as to beadjacent to one another, to collectively performing the tightening of aplurality of screws disposed with a pitch narrower than a pitch betweenthe motors.

Further, in such an offset-type screw tightening apparatus, generally, amotor output is transmitted to an output shaft connected to a bit via atrain of gears.

The output shaft is pressed down by a spring force in order to preventthe engagement between the bit and the recess from being canceled inscrew tightening. Therefore, it is necessary for the output shaft tosimultaneously perform two axial motions of rotation and axial sliding.

Conventionally, as a configuration enabling an output shaft to performtwo axial motions of rotation and sliding, the following configurationis general. A hole is formed in the center of a gear (hollow gear)receiving a driving force from a motor, and an output shaft is made topass through the hole. A key axially extending is provided to an innercircumference of the hollow gear, and this key is engaged with a keygroove formed on the output shaft. With this configuration, the hollowgear and the output shaft are integrally rotatable due to splinecoupling, and the output shaft is slidable along the hollow gear.Japanese Unexamined Utility Model Application Publication No. 6-53037discloses a screw tightening apparatus having the similar configuration.

Meanwhile, in accordance with miniaturization of products such asprecision apparatuses in recent years, screws used for the products areminiaturized, which results in a narrower pitch among screws. In orderto tighten such fine screws disposed at an extremely narrow pitch, it isnecessary to make diameters of a bit and an output shaft to which thebit is connected as well small.

However, as a diameter of the output shaft becomes small, it isdifficult to precisely form a key groove on the output shaft. Even if akey groove can be precisely formed therein, because a width thereof ismade extremely narrow, transmission of a sufficient torque from thehollow gear may be impossible.

Further, many products such as precision apparatuses into which screwsare tightened include parts vulnerable to static electricity. Therefore,it is necessary to prevent static electricity generated on the bit andhaving harmful effects on the products from flowing into the products.

The output shaft is supported rotatably by ball bearings fixed to a mainbody of the screw tightening apparatus. However, some grease is providedamong metal parts constituting the ball bearing, which reduceselectrical conductivity therebetween.

Further, since some grease is applied between the hollow gear and theoutput shaft in order to make relative sliding thereof smooth in manycases, the electrical conductivity from the output shaft to the hollowgear as well is reduced. As described above, conventionally, it has beendifficult to secure a route through which the static electricitygenerated on the bit is effectively flowed out.

Japanese Patent Laid-Open No. 2001-293666 discloses a configurationdesigned to eliminate static electricity from a screw tighteningapparatus. Japanese Patent Laid-Open No. 2001-293666 discloses aconfiguration in which a conductive brush along which an outercircumference of a rotating output shaft is slidable is attached to abearing case and a motor block which constitute a main body of theapparatus. However, in the screw tightening apparatus disclosed inJapanese Patent Laid-Open No. 2001-293666, the conductive brush attachedto the main body of the apparatus touches the outer circumference of theoutput shaft which does not axially move with respect to the main body.Therefore, if this configuration is directly applied to a screwtightening apparatus whose output shaft axially moves, inconveniencesuch as an axial deformation of the conductive brush may be caused.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a screw tightening apparatus that iseasily processed and capable of transmitting a sufficient torque to evenan output shaft having a small diameter. Further, the present inventionprovides a screw tightening apparatus that is capable of obtaining goodconductivity from an output shaft axially movable to a main body of theapparatus, and certainly eliminating static electricity generated on abit.

A screw tightening apparatus according to another aspect of the presentinvention includes a motor, an output shaft to which a bit for screwtightening is connected so as to be rotatable integrally with the outputshaft and which is axially movable, the output shaft being driven to berotated by the motor, a spring whose one end contacts a memberconstituting a main body of the screw tightening apparatus, and a springreceiving member which the other end of the spring contacts andtransmits a biasing force of the spring to the output shaft. The screwtightening apparatus further includes a conductive member which contactsthe output shaft and the spring receiving member.

This configuration enables static electricity generated on the bit tocertainly flow into the main body of the apparatus (ground) via theoutput shaft, the conductive member, the spring receiving member, andthe spring. Additionally, since the conductive member is in contact withthe output shaft and the spring receiving member which do not relativelymove, even when the output shaft rotates, the electrical conductivitytherebetween can be favorably maintained. Further, since an axial forcedoes not act on the conductive member, axial deformation of theconductive member and deterioration in the electrical conductivityassociated therewith can be avoided.

A configuration may be employed in which the conductive member is fixedto the output shaft and slidable to the spring receiving member duringrotation of the output shaft. Since the diameter of the spring receivingmember is larger than that of the output shaft, the conductive membercan be stably slidable with respect to the spring receiving memberduring the rotation of the output shaft.

Further, it is preferable that the conductive member is disposed at aninner side of the spring so as to be in contact with the output shaftand the spring receiving member. This configuration enables effectiveutilization of a space between the spring and the output shaft or thespring receiving member, and thus making it possible to provide theconductive member without an increase in size of the screw tighteningdriver.

Other aspects of the present invention will become apparent from thefollowing description and the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external view of a screw tightening system that is a firstembodiment (Embodiment 1) of the present invention.

FIG. 2 is a block diagram illustrating a control system of the screwtightening system of Embodiment 1.

FIG. 3A is a plan view of a hard disk drive onto which screw tighteningis performed by the screw tightening system of Embodiment 1.

FIG. 3B is a side view of the hard disk drive shown in FIG. 3A.

FIG. 4 is a timing chart showing the operations of the screw tighteningsystem of Embodiment 1.

FIG. 5 is a block diagram showing the configuration of a motor controlunit of the screw tightening system of Embodiment 1.

FIG. 6 is a table showing the examples of settings of a wait timer andthe like in the screw tightening system of Embodiment 1.

FIG. 7A is a flowchart showing the operations of the control system ofthe screw tightening system of Embodiment 1.

FIG. 7B is a flowchart showing the operations of the control system ofthe screw tightening system of Embodiment 1.

FIG. 7C is a flowchart showing the operations of the control system ofthe screw tightening system of Embodiment 1.

FIG. 8 is a block diagram showing the configuration of a control systemof a screw tightening system that is a second embodiment (Embodiment 2)of the present invention.

FIG. 9 is a block diagram showing the configuration of a control systemof a positioning system that is a third embodiment (Embodiment 3) of thepresent invention.

FIG. 10 is a timing chart showing the synchronization control operationsof Embodiment 3.

FIG. 11 is an external view of a torque measurement apparatus that is afourth embodiment (Embodiment 4) of the present invention.

FIG. 12 is a block diagram showing the configuration of the torquemeasurement apparatus of Embodiment 4.

FIG. 13 is a flowchart showing the control operations of the torquemeasurement apparatus of Embodiment 4.

FIG. 14 illustrates an example of a torque measurement result by thetorque measurement apparatus of Embodiment 4.

FIG. 15 is a block diagram showing the configuration of a torquefluctuation correction system that is a fifth embodiment (Embodiment 5)of the present invention.

FIG. 16A is a flowchart showing a torque fluctuation correctionprocedure of Embodiment 5.

FIG. 16B illustrates an example of torque correction data used in thetorque fluctuation correction system of Embodiment 5.

FIG. 17 illustrates an example of torque measurement results before andafter correction by the torque fluctuation correction system ofEmbodiment 5.

FIG. 18 is a sectional view showing the configuration of a screwtightening driver that is a sixth embodiment (Embodiment 6) of thepresent invention.

FIG. 19 is an enlarged sectional view showing a portion of theconfiguration of the screw tightening driver of Embodiment 6.

FIG. 20 is a perspective view showing a portion of the configuration ofthe screw tightening driver of Embodiment 6.

FIG. 21 is a perspective view showing the configuration of a screwtightening driver that is a seventh (Embodiment 7) of the presentinvention.

FIG. 22 is a block diagram showing configuration examples of a screwtightening system to which the screw tightening driver of Embodiment 7is applied.

FIG. 23 is a sectional view showing the configuration of a screwtightening driver that is an eighth embodiment (Embodiment 8) of thepresent invention.

FIG. 24 is a sectional view showing a modified example of the screwtightening driver of Embodiment 8.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary embodiments of the present invention will hereinafter bedescribed with reference to the accompanying drawings.

Embodiment 1

FIG. 1 illustrates the schematic configuration of a screw tighteningsystem that is Embodiment 1 of the present invention. Reference numeral1 denotes the entire screw tightening system of this embodiment.Reference numeral 2 denotes a main body of the screw tightening system 1(hereinafter referred to as an apparatus main body). Reference numeral 3denotes a lifting mechanism attached to the apparatus main body 2, thelifting mechanism moving a support table 4 up and down.

Plural (four in FIG. 1) screw tightening drivers (screw tighteningapparatuses) D are attached on a horizontal plate 4 a of the supporttable 4. Each of these screw tightening drivers D rotates a screwtightening bit B extending downward from the horizontal plate 4 athrough a through-hole 4 c formed in the horizontal plate 4 a. Thesescrew tightening drivers D perform screw tightening operations withrespect to a workpiece (an object for screw tightening) (not shown)which is disposed beneath the horizontal plate 4 a.

FIG. 1 illustrates the four screw tightening drivers D. However, thisnumber of the screw tightening drivers is an example, three or less, orfive or more screw tightening drivers may be provided.

Reference symbol MC denotes a main controller which transmits anoperation start command and the like to a servo controller SC providedto each of the drivers D. The main controller MC is constituted by acomputer.

FIG. 2 illustrates the schematic configuration of a control system ofthe screw tightening system. Description herein will be made of a casein which six screw tightening drivers (first to sixth screw tighteningdrivers) D1 to D6 are controlled. However, FIG. 2 illustrates only thefirst, second, and sixth screw tightening drivers D1, D2, and D6.

Each screw tightening driver includes a motor M serving as a drivingsource, the screw tightening bit B whose lower end (tip end) engageswith a recess formed on a screw head, and a bit driving unit BD thatdrives the bit B by a driving force transmitted from the motor M.Although not shown in the drawing, an output shaft to which the bit B isdetachably connected is disposed in the bit driving unit BD.

In the drawing, a casing C holding the motor M and the bit driving unitBD contains a train of reduction gears that transmits a driving force toa driving gear rotating integrally with the output shaft from an inputgear attached to the output shaft of the motor M. A brush motor or abrushless motor may be used as the motor M.

Reference symbol SC denotes the servo controller that directly controlsthe driving of each of the screw tightening drivers shown also in FIG.1, the servo controller SC being provided to each of the screwtightening drivers.

Reference symbol MC denotes the main controller shown also in FIG. 1which transmits various types of operation commands to the six servocontrollers SC via a communication line IL.

The servo controller SC includes a synchronization control unit C1connected to first and second wired OR lines OR1 and OR2, a motorcontrol unit C2 that controls a voltage or an electric current to beapplied to the motor M. The motor control unit C2 includes a calculatingunit CAL constituted by a CPU or the like. Moreover, the servocontroller SC includes first and second transistors TR1 and TR2constituting an input and output circuit between the synchronizationcontrol unit C1 and the first and second wired OR lines OR1 and OR2. Thefirst and second transistors TR1 and TR2 include open collectors thatrespectively perform output to the first and second wired OR lines OR1and OR2.

In this embodiment, a wired OR circuit (a circuit serving as an OR gatein a negative logic by directly leading an output of a TTL logicthereto) is formed by using the open collector output of the transistor.However, the wired OR circuit may be formed by using an open drainoutput of a CMOS in place of the transistor.

Further, as shown in FIG. 2, a pull-up resister PR is connected to oneends of the first and second wired OR lines OR1 and OR2.

The synchronization control unit C1 includes an odd line input circuitand an odd line output circuit which are connected to the first wired ORline OR1, and an even line input circuit and an even line output circuitwhich are connected to the second wired OR line OR2. The term “odd lineoutput circuit” and “even line output circuit” are circuits that outputsignals indicating the odd numberth and even numberth synchronizationwaiting states in the screw tightening drivers D1 to D6, and the term“odd line input circuit” and “even line input circuit” are circuits todetect the states of the first wired OR line OR1 and the second wired ORline OR2.

The screw tightening system formed in this way is used for a clamp screwtightening process for a magnetic disk serving as a workpiece shown in,for example, FIGS. 3A and 3B, in a hard disk drive. FIG. 3A is a planview of a magnetic disk part 20 in the hard disk drive, and FIG. 3B is aside view thereof.

The magnetic disk part 20 includes two magnetic disks 21 overlappedabove and below so as to sandwich a spacer 22, and a spindle motor 23that rotates the magnetic disks 21. A bearing 24, the magnetic disks 21,and the spacer 22 are disposed to be laminated concentrically around theouter circumference of the spindle motor 23, and a clamp plate 25 isdisposed on the upper magnetic disk 21. As shown in FIG. 3A, the clampplate 25 is connected to a rotation output part of the spindle motor 23with six screws SR respectively disposed at apex positions of a regularhexagon. With this arrangement, the magnetic disks 21 rotate along withthe rotation of the spindle motor 23, and data are written on themagnetic disks 21 or the written data are read by a magnetic read andwrite means (not shown). In this embodiment, the six screws SR are allright-handed screws. However, all the screws SR may be left-handedscrews.

In this embodiment, when the screw tightening for the clamp plate 25 isperformed, first, each screw is tightened until the screw head comesinto contact with (seats on) the clamp plate 25, and thereafter, thetightening torque of each screw is increased step by step up to thefinal tightening torque. At this time, the six screws SR are dividedinto three pairs such that two screws in a diagonal positionrelationship in FIG. 3A are made into a pair. That is, among the firstto sixth screws SR denoted with the numbers 1 to 6 in FIG. 3A, the firstand second screws SR are made into a pair, and the third and fourthscrews SR are made into a pair. Moreover, the fifth and sixth screws SRare made into a pair. Then, the tightening of the two screws in the samepair to the seating on the clamp plate 25 (hereinafter referred tosimply as the seating) and the step-by-step increase of the tighteningtorque thereafter are simultaneously performed. On the other hand, amongthese pairs, the start of the screw tightening to the seating and thestart of the increase of the tightening torque at each step are made tohave a time difference. The tightenings of the first to sixth screws SRare respectively performed by the first to sixth screw tighteningdrivers D1 to D6. Namely, the drivers D1 and D2 as one pair, the driversD3 and D4 as another pair, and the drivers D5 and D6 as still anotherpair are respectively controlled synchronously.

However, a screw tightening method for the clamp plate 25 is not limitedthereto. For example, the first to sixth screws SR may be made to seaton the clamp plate 25 in this order (in a star-shaped order) first, andthereafter the tightening torques thereof may be increased step by stepin the same order. Further, the six screws SR may be divided into twogroups including three screws SR which are not adjacent to one another(for example, the first, fourth, and fifth screws SR, and the second,third, and sixth screws SR), and the tightening of the three screws inthe same group to the seating and the step-by-step increase of thetightening torque thereafter may be simultaneously performed, and on theother hand, between these groups, the start of the screw tightening tothe seating and the start of the increase of the tightening torque ateach step may be made to have a time difference.

Further, in this embodiment, description is made of a case in which theclamp tightening is performed with the six screws SR. However, in thepresent invention, the number of screws may be an odd number or an evennumber other than six.

FIG. 4 shows a control procedure and operation timings of a seatingoperation and a tightening torque increase operation in the clamptightening synchronization control when the above-described two driversare made into a pair.

In FIG. 4, (a) to (c) show the changes in motor voltage command valuesin the seating operations and the tightening torque increase operations(hereinafter simply referred to as the torque increase operations) bythe screw tightening drivers in the respective pairs. The motor voltagecommand value may be considered to be proportional to an output torqueof the screw tightening driver. Further, In FIG. 4, (d) to (f) show theoperating states of the screw tightening drivers in the respectivepairs.

In FIG. 4, (a) to (i) inscribe the first and second screw tighteningdrivers D1 and D2 that tighten the first and second screws SR and theservo controller SC that controls the first and second screw tighteningdrivers D1 and D2 as “DRIVER 1, DRIVER 2”, the third and fourth screwtightening drivers D3 and D4 that tighten the third and fourth screws SRand the servo controller SC that controls the third and fourth screwtightening drivers D3 and D4 as “DRIVER 3, DRIVER 4”, and the fifth andsixth screw tightening drivers D5 and D6 that tighten the fifth andsixth screws SR and the servo controller SC that controls the fifth andsixth screw tightening drivers D5 and D6 as “DRIVER 5, DRIVER 6”. Thenames will be used in the following description.

Further, in FIG. 4, (g) to (i) show the outputting states of the evenand odd lines in the servo controllers SC provided to the drivers in therespective pairs. Moreover, (j) shows the states of the second wired ORline (hereinafter referred to as the even wired OR line) OR2 and thefirst wired OR line (hereinafter referred to as the odd wired OR line)OR1.

In (g) to (i), since the negative logic is used in this embodiment, ahigher signal level corresponds to an off-state (inactive or H level),and a lower signal level corresponds to an on-state (active or L level).

When a start-up waiting signal from the main controller MC istransmitted to the respective servo controllers SC, each servocontroller SC performs a start-up waiting operation including a start-upoperation of the motor control unit C2, an operation for confirming aninitialization state of the synchronization control unit C1 and thelike. Further, the main controller MC transmits command data describingoperations at respective synchronization points which will be describedlater to each driver (servo controller SC) through the communicationline IL. Each driver stores the command data in a memory such as a flashmemory or an EEPROM. After setting (judging or detecting) the respectivesynchronization points, each driver operates in accordance with thecommand data stored in the memory.

In the start-up waiting operation, due to the initialization operationwhich will be described later, the even line outputs of the drivers 1 to6 in all the pairs are in an off-state, and the odd line outputs thereofare in an on-state. Further, in accordance therewith, the even wired ORline OR2 is in an off-state, and the odd wired OR line OR1 is in anon-state.

Further, the motor control unit C2 (calculating unit CAL) has a counterfunction of counting the number of times of synchronization waitingstates, which will be described later. This synchronization waitingcounter is set to 0 by the initialization operation which will bedescribed later. The main controller MC may have a synchronizationwaiting counter function, and may receive information on a count valueof the synchronization waiting counter via communication from eachdriver.

Moreover, in this start-up waiting operation, the settings of the screwsSR for the respective drivers and screw holes formed in the magneticdisk unit 20 are performed.

When each driver receives a start-up signal from the main controller MC,the driver increments the synchronization waiting counter by one from 0.Then, the driver switches the even line output into an on-state, andswitches the odd line output into an off-state. FIG. 4 shows a case inwhich the start-up operation of the drivers 5 and 6 takes a time longerthan those of the other drivers due to a transmission time difference ofthe start-up signal from the main controller MC, variations in operationcharacteristics of the respective drivers and the like.

When the start-up waiting operation of any one of the drivers 1 to 6 iscompleted, and thus the even line output of the driver comes into theon-state, the odd wired OR line OR1 is still in the on-state, and on theother hand, the even wired OR line OR2 is switched from the off-stateinto an on-state.

When the start-up waiting operations of all the drivers 1 to 6 arecompleted, the even wired OR line OR2 is still in the on-state, and theodd wired OR line OR1 is switched from the on-state into the off-state.

Each driver sets a point in time when the odd wired OR line OR1 isswitched from the on-state into the off-state, to an odd numberthsynchronization point (where this is a synchronization point 1).

Then, immediately after setting the synchronization point 1, the drivers1 and 2 rotate the motor M to tighten the first and second screws SRuntil they seat on the clamp plate 25 (hereinafter this operation isreferred to as the seating operation).

FIG. 5 illustrates part of the circuit configuration in the motorcontrol unit C2 in each driver. In FIG. 5, reference symbol M denotes amotor, and reference symbol T denotes a tachometer generator providedfor detecting a rotational speed of the motor M. An analog signal outputfrom the tachometer generator T is converted into a digital signalindicating the rotational speed by an A/D converter AD2, to be input tothe calculating unit (CPU or the like) CAL in the motor control unit C2.

Further, reference symbol DA denotes a D/A converter that converts amotor voltage command value input as a digital signal via thecalculating unit CAL from the memory into an analog signal. An outputsignal from the D/A converter DA is amplified to a predetermined levelby an amplifier A to be applied to the motor M. With this signal, themotor M rotates at a speed corresponding to the motor voltage commandvalue or in a torque output state. An A/D converter AD1 that converts ananalog value of electric current (motor current) flowing in the motor Minto a digital value is connected to the motor M. An output from the A/Dconverter AD1 is input to the calculating unit CAL.

In accordance with the configuration of FIG. 5, the driver rotates witha small current corresponding to a frictional torque acting between thescrew SR and the screw hole of the clamp plate 25 until the screw SRseats on the clamp plate 25. At this time, since speed feedback isautomatically applied to the motor M by a counter-electromotive forcegenerated in the motor M, the motor voltage command value and the motorrotational speed are approximately proportion to each other (where aproportional constant is a counter-electromotive force constant).

Since the rotation of the driver is suddenly stopped after the screw SRseats on the clamp plate 25, the counter-electromotive force in themotor M reduces to approximately zero. Therefore, the motor voltagecommand value and the motor rotational speed come to be approximatelyproportional to one another.

Accordingly, during the rotation until the screw SR seats on the clampplate 25, the motor voltage command value is a command value of themotor rotational speed, and after the screw SR seats on the clamp plate25, the motor voltage command value becomes a command value of motorcurrent, i.e., an output torque. Where the proportional constant is asum of all resistance components, such as a motor wire wound resistanceand a resistance for current measurement, which are connected to themotor M in series.

When more precise rotational speed control and torque control arerequired independently of the counter-electromotive force constant andthe resistance value, the signal from the tachometer generator T may befed back or the current measurement value by the A/D converter AD1 maybe fed back. The detection of the rotational speed may be performed onthe basis of an inverse number of a time interval measurement value ofan output pulse signal from a rotary encoder, which is used in place ofthe tachometer generator.

Even when the motor M is a brushless motor, performing electricalcommutation control using a signal from a hall element, a rotary encoderor the like in place of a mechanical brush enables control of arotational speed and a torque as is the case with a brush motor.

The seating of the screw SR can be determined by detecting that therotational speed measurement value by the tachometer generator T, therotary encoder or the like reduces to be equal to or lower than aspecified value. Further, it may be determined by detecting that theelectric current applied to the motor (motor current) rapidly increasesin the measurement thereof, i.e., the torque increases.

During the period of “rotation→→→seating” shown in FIG. 4, the motor Mis caused to rotate by providing a motor voltage command value forobtaining a desired rotational speed of the motor as a target value, andthe voltage is raised up to the target value at a specified voltagechange rate. Then, during counting of a specified hold time (i.e.,during a hold period), that voltage is kept to continue the rotation.

A time required for the seating of the screws plus some extra time a maybe set to the hold time, and completion of the counting-up of the holdtime may be regarded as completion of the seating. However, the start ofthe torque increase after the seating is delayed by the extra time aserving as a margin time. In such a case, programming so as to escapefrom the hold period by the above-described seating determination methodbased on the rotational speed or the motor current enables immediatestart of the torque increase after seating. When the seating is notdetected even after the hold time has been elapsed, an error may bedetermined to stop the screw tightening.

Again in FIG. 4, when the seating of the first and second screws SR isdetected, the drivers 1 and 2 enter a waiting state for the followingeven numberth synchronization point 2. At this time, the calculatingunits CAL of the drivers 1 and 2 cause the synchronization waitingcounter to increment by one from 1 to 2. Further, the drivers 1 and 2switch the even line outputs from the on-state into the off-state, andswitch the odd line outputs from the off-state into the on-state. Withthis switching, the even wired OR line OR2 is still in the on-state, andon the other hand, the odd wired OR line OR1 is switched from theoff-state into the on-state. In this synchronization waiting state, thedrivers 1 and 2 maintain the output torque at the point in time when theseating operations are completed.

Further, the drivers 3 and 4 and the drivers 5 and 6 start countingpredetermined wait times from the synchronization point 1. The wait timein the drivers 5 and 6 is set to a time longer than that of the waittime in the drivers 3 and 4.

When the wait time has elapsed, the drivers 3 and 4 start the seatingoperations in the same way as the drivers 1 and 2.

FIG. 4 shows the case in which the seating operations of the drivers 3and 4 are started slightly before the completion of the seatingoperations of the drivers 1 and 2. When the seating operations of thedrivers 3 and 4 are completed (the seating of the third and fourthscrews SR is detected), the drivers 3 and 4 enter a waiting state forthe following synchronization point 2. At this time, the calculatingunits CAL of the drivers 3 and 4 cause the synchronization waitingcounter to increment by one from 1 to 2. Further, the drivers 3 and 4switch the even line outputs from the on-state into the off-state, andswitch the odd line outputs from the off-state into the on-state. Atthis point in time, the even wired OR line OR2 is still in the on-state,and the odd wired OR line OR1 as well is still in the on-state. In thissynchronization waiting state, the drivers 3 and 4 also maintain theoutput torque at the point in time when the seating operations arecompleted.

Further, when the wait time has elapsed, the drivers 5 and 6 start theseating operations. FIG. 4 shows the case in which the seatingoperations of the drivers 5 and 6 are started slightly before thecompletion of the seating operations of the drivers 3 and 4 (however,after the completion of the seating operations of the drivers 1 and 2).When the seating operations are completed (the seating of the fifth andsixth screws SR is detected), the drivers 5 and 6 enter a waiting statefor the following synchronization point 2. At this time, the calculatingunits CAL of the drivers 5 and 6 cause the synchronization waitingcounter to increment by one from 1 to 2. Further, the drivers 5 and 6switch the even line outputs from the on-state into the off-state, andswitch the odd line outputs from the off-state into the on-state. Withthis switching, the even wired OR line OR2 is switched from the on-stateinto the off-state. On the other hand, the odd wired OR line OR1 isstill in the on-state. Thereafter, the drivers 5 and 6 also maintain theoutput torque at the point in time when the seating operations arecompleted.

Each driver sets the synchronization point 2 in accordance with theswitching of the even wired OR line OR2 from the on-state into theoff-state.

The drivers 1 and 2 start increasing the motor voltage command values(torque increase operations) up to a value corresponding to the firsttarget torque immediately after setting the synchronization point 2.With this operation, the output torques of the drivers 1 and 2 and thetightening torques of the first and second screws SR begin to graduallyincrease. Further, the drivers 3 and 4 and the drivers 5 and 6 startcounting the wait times from the synchronization point 2. The wait timeof the drivers 5 and 6 is set to a time longer than that of the waittime of the drivers 3 and 4. This is the same as at the respective stepsin the following torque increase.

When the output torque increases up to the first target torque, i.e.,when the motor voltage command value increases up to the first targettorque, the drivers 1 and 2 enter a waiting state for the following oddnumberth synchronization point 3. At this time, the calculating unitsCAL of the drivers 1 and 2 cause the synchronization waiting counter toincrement by one from 2 to 3. Further, the drivers 1 and 2 switch theeven line outputs from the off-state into the on-state, and switch theodd line outputs from the on-state into the off-state. With thisswitching, the even wired OR line OR2 is switched from the off-stateinto the on-state. On the other hand, the odd wired OR line OR1 is stillin the on-state.

In this synchronization waiting state, the drivers 1 and 2 maintain theincreased output torque (the first target torque). This time formaintaining the torque is resulted by providing the wait times to thedrivers in the other pairs. The torque can be sufficiently stabilizedduring this time. This is the same as the drivers in the other pairs.

When the wait time has elapsed, the drivers 3 and 4 start the torqueincrease operations up to the first target torque in the same way as thedrivers 1 and 2. FIG. 4 shows the case in which the torque increaseoperations of the drivers 3 and 4 are started nearly simultaneously withthe completion of the torque increase operations of the drivers 1 and 2.When the torque increase operations are completed, the drivers 3 and 4enter a waiting state for the following synchronization point 3. At thistime, the calculating units CAL of the drivers 3 and 4 cause thesynchronization waiting counter to increment by one from 2 to 3.Further, the drivers 3 and 4 switch the even line outputs from theoff-state into the on-state, and switch the odd line outputs from theon-state into the off-state. At this point in time, the even wired ORline OR2 is still in the on-state, and the odd wired OR line OR1 as wellis still in the on-state. In this synchronization waiting state, thedrivers 3 and 4 as well maintain the output torque (the first targettorque) at the point in time when the torque increase operations arecompleted.

Moreover, when the wait time has elapsed, the drivers 5 and 6 start thetorque increase operations up to the first target torque. FIG. 4 showsthe case in which the torque increase operations of the drivers 5 and 6are started slightly before the completion of the torque increaseoperations of the drivers 3 and 4 (however, after the completion of thetorque increase operations of the drivers 1 and 2). When the torqueincrease operations are completed, the drivers 5 and 6 enter a waitingstate for the following synchronization point 3. At this time, thecalculating units CAL of the drivers 5 and 6 cause the synchronizationwaiting counter to increment by one from 2 to 3. Further, the drivers 5and 6 switch the even line outputs from the off-state into the on-state,and switch the odd line outputs from the on-state into the off-state.With this switching, the even wired OR line OR2 is still in theon-state, and on the other hand, the odd wired OR line OR1 is switchedfrom the on-state into the off-state. Thereafter, the drivers 5 and 6 aswell maintain the output torque (the first target torque) at the pointin time when the torque increase operations are completed.

FIG. 4 shows the state in which the torque increase operations of thedrivers in the respective pairs are simultaneously completed. However,in reality, a time required for the torque increase operation for eachdriver differs due to a variation in the operation characteristics ofthe servo controller SC and the motor M in many cases. In this case,even in the drivers in the same pair, the switching of the even lineoutput and the odd line output in one driver in which the torqueincrease operation is earlier completed is performed earlier than thatin the other driver in which the torque increase operation is notcompleted. However, since the state of the wired OR line to be switchedis switched at a point in time when the last driver completes the torqueincrease operation, the synchronization point is set after thecompletion of the torque increase operations of all the drivers.

Each driver sets the synchronization point 3 in accordance with theswitching of the odd wired OR line OR1 from the on-state into theoff-state.

The drivers 1 and 2 start the torque increase operations up to a secondtarget torque immediately after setting the synchronization point 3.Further, the drivers 3 and 4 and the drivers 5 and 6 start counting thewait times from the synchronization point 3.

In the drivers 1 and 2, when the output torque increases up to thesecond target torque, i.e., when the motor voltage command valueincreases up to a value corresponding to the second target torque, thedrivers 1 and 2 enter a waiting state for the following even numberthsynchronization point 4. At this time, the calculating units CAL of thedrivers 1 and 2 cause the synchronization waiting counter to incrementby one from 3 to 4. Further, the drivers 1 and 2 switches the even lineoutputs from the on-state into the off-state, and switches the odd lineoutputs from the off-state into the on-state. With this switching, theeven wired OR line OR2 is still in the on-state, and on the other hand,the odd wired OR line OR1 is switched from the off-state into theon-state. In this synchronization waiting state, the drivers 1 and 2maintain the increased output torque (the second target torque).

When the wait time has elapsed, the drivers 3 and 4 start the torqueincrease operations up to the second target torque. When the torqueincrease operations are completed, the drivers 3 and 4 enter a waitingstate for the following synchronization point 4. At this time, thecalculating units CAL of the drivers 3 and 4 cause the synchronizationwaiting counter to increment by one from 3 to 4. The drivers 3 and 4switches the even line outputs from the on-state into the off-state, andswitches the odd line outputs from the off-state into the on-state. Atthis point in time, the even wired OR line OR2 is still in the on-state,and the odd wired OR line OR1 as well is still in the on-state. In thissynchronization waiting state, the drivers 3 and 4 as well maintain theincreased output torque (the second target torque).

Moreover, when the wait time has elapsed, the drivers 5 and 6 start thetorque increase operations up to the second target torque. When thetorque increase operations are completed, the drivers 5 and 6 enter awaiting state for the following synchronization point 4. At this time,the calculating units CAL of the drivers 5 and 6 cause thesynchronization waiting counter to increment by one from 3 to 4. Thedrivers 5 and 6 switches the even line outputs from the on-state intothe off-state, and switches the odd line outputs from the off-state intothe on-state. With this switching, the even wired OR line OR2 isswitched from the on-state into the off-state. On the other hand, theodd wired OR line OR1 is still in the on-state. Thereafter, the drivers5 and 6 as well maintain the output torque (the second target torque) atthe point in time when the torque increase operations are completed.

Each driver sets the synchronization point 4 in accordance with theswitching of the even wired OR line OR2 from the on-state into theoff-state.

The drivers 1 and 2 start the torque increase operations up to a thirdtarget torque immediately after setting the synchronization point 4.Further, the drivers 3 and 4 and the drivers 5 and 6 start the torqueincrease operations up to the third target torque after the respectivewait time has elapsed. In accordance with the completion of the torqueincrease operation, each driver enters a waiting state for the followingsynchronization point 5, and the synchronization waiting counters is setto 5. Further, each driver switches the even line output from theoff-state into the on-state, and switches the odd line output from theon-state into the off-state. Due to the switching of the even lineoutput in one of the drivers from the off-state into the on-state, theeven wired OR line OR2 is switched from the off-state into the on-state.

Then, in accordance with the completion of the torque increaseoperations of the drivers 5 and 6, the even wired OR line OR2 is stillin the on-state, and on the other hand, the odd wired OR line OR1 isswitched from the on-state into the off-state. Each driver maintains theoutput torque (the third target torque) at the point in time when thetorque increase operations are completed.

Each driver sets the synchronization point 5 in accordance with theswitching of the odd wired OR line OR1 from the on-state into theoff-state.

The drivers 1 and 2 start the torque increase operations up to the finaltarget torque immediately after setting the synchronization point 5.Further, the drivers 3 and 4 and the drivers 5 and 6 start torqueincrease operations up to the final target torque after the respectivewait time has elapsed.

At the torque increase step up to the final target torque, in order tostabilize the tightening states of the screws SR by the final targettorque after the output torque reaches the final target torque, eachdriver enters a waiting state for the following synchronization point 6after the counting of the predetermined hold time is completed, and setsthe synchronization waiting counter to 6. Moreover, each driver switchesthe even line output from the on-state into the off-state, and switchesthe odd line output from the off-state into the on-state. Due to theswitching of the odd line output in one of the drivers from theoff-state into the on-state, the odd wired OR line OR1 is switched fromthe off-state into the on-state.

Then, in accordance with the completion of the torque increaseoperations of the drivers 5 and 6 and the counting-up of the hold time,the even wired OR line OR2 is switched from the on-state into theoff-state. On the other hand, the odd wired OR line OR1 is still in theon-state.

Each driver sets the synchronization point 6 in accordance with theswitching of the even wired OR line OR2 from the on-state into theoff-state. The drivers 1 and 2 start torque reduction operations byreducing the motor command value immediately after setting thesynchronization point 6. Further, the drivers 3 and 4 and the drivers 5and 6 start the torque reduction operations after the respective waittime has elapsed.

In accordance with the completion of the torque reduction operation,each driver enters a waiting state for the following synchronizationpoint 7, and sets the synchronization waiting counter to 7. Moreover,each driver switches the even line output from the off-state into theon-state, and switches the odd line output from the on-state into theoff-state. Due to the switching of the even line output in one of thedrivers from the off-state into the on-state, the even wired OR line OR2is switched from the off-state into the on-state.

Then, in accordance with the completion of the torque reductionoperations of the drivers 5 and 6, the even wired OR line OR2 is stillin the on-state, and on the other hand, the odd wired OR line OR1 isswitched from the on-state into the off-state.

Each driver sets the synchronization point 7 in accordance with theswitching of the odd wired OR line OR1 from the on-state into theoff-state. Each driver resets the count value of the synchronizationwaiting counter to 0 in accordance with the setting of thesynchronization point 7. Moreover, each driver switches the even lineoutput from the on-state into the off-state, and switches the odd lineoutput from the off-state into the on-state. With this switching, theeven wired OR line OR2 is switched from the on-state into the off-state,and the odd wired OR line OR1 is switched from the off-state into theon-state. This operation is the aforementioned initialization operation.Thus, a series of the screw tightening operations are completed.

In this embodiment, the initialization operation is performed when thescrew tightening operation is completed. However, an initializationoperation may be performed during the start-up waiting operation.

Tables in FIG. 6 show the examples of settings of the wait times (waittimer values), the motor voltage command target values (target torques),and the hold times (hold timer values) from the respectivesynchronization points of the drivers 1 and 2, the drivers 3 and 4, andthe drivers 5 and 6. Further, the tables show time-out times forcancelling the synchronization waiting states, distinctions betweencontinuance and termination of the synchronization processing in aseries of the screw tightening operations, change rates of the motorvoltage command values in the torque increase/reduction operation, andthe presence or absence of escaping from the hold state based on adetection of seating as well as examples.

In FIG. 6, the wait timer values at the respective steps in the drivers3 and 4 and the drivers 5 and 6 are set to be the same. However, thesevalues may be set to be different from one another.

FIGS. 7A to 7C show programs for controlling the operations relating tosynchronization, which are computer programs executed by the servocontroller SC (or the calculating unit CAL) in each driver.

FIG. 7A is a flowchart showing the control of the initializationoperation in each driver performed at the time of terminating the seriesof the screw tightening operations in this embodiment. First, at step(which is abbreviated as S in the figure) 61, the servo controller SCstarts the initialization operation by setting the synchronization point7. At step 62, the servo controller SC (calculating unit CAL) resets thecount value of the synchronization waiting counter to 0.

Next, at step 63, the servo controller SC sets the even line output tothe off-state, and sets the odd line output to the on-state. In thissetting, the even wired OR line OR2 is set to the off-state, and the oddwired OR line OR1 is set to the on-state. Then, this initializationoperation is completed at step 64.

FIG. 7B is a flowchart relating to the settings for the states of theeven and odd line outputs, which are executed immediately after thecompletion of the seating operation and the completion of the torqueincrease/reduction operations in each driver. First, when the completionof the seating operation and the completion of the torqueincrease/reduction operations are detected at step 65, the routineproceeds to step 66.

At step 66, the servo controller SC (calculating unit CAL) incrementsthe count value of the synchronization waiting counter by one. Next, atstep 67, the servo controller SC determines whether the count value ofthe synchronization waiting counter is an odd number or an even number.When the count value is an odd number, the routine proceeds to step 68where the servo controller SC sets the even line output to the on-state,and sets the odd line output to the off-state. When all the drivers comeinto this state, the even wired OR line OR2 is in the on-state, and onthe other hand, the odd wired OR line OR1 is switched from the on-stateinto the off-state.

On the other hand, when the count value of the synchronization waitingcounter is an even number, the routine proceeds to step 69 where theservo controller SC sets the even line output to the off-state, and setsthe odd line output to the on-state. When all the drivers come into thisstate, the odd wired OR line OR1 is in the on-state, and on the otherhand, the even wired OR line OR2 is switched from the on-state into theoff-state.

FIG. 7C shows a flowchart for a synchronization determination operation.The synchronization determination operation is started at step 71, andnext at step 72, the servo controller SC determines whether the countvalue of the synchronization waiting counter is an odd number or an evennumber. When the count value is an odd number, the routine proceeds tostep 73. At step 73, the servo controller SC determines whether the oddwired OR line OR1 is in the on-state or the off-state. When the oddwired OR line OR1 is in the on-state, step 73 is repeated. Further, whenthe odd wired OR line OR1 is in the off-state, the routine proceeds tostep 75 only in a case where the odd wired OR line OR1 was determined asin the on-state in the previous routine. At step 75, the servocontroller SC determines that the current state is a state to besynchronized, and sets a synchronization point of a number which is thesame as the count value of the synchronization waiting counter. Then,the routine returns to step 72.

On the other hand, when the servo controller SC determined that thecount value of the synchronization waiting counter is an even number atstep 72, the routine proceeds to step 74. At step 74, the servocontroller SC determines whether the even wired OR line OR2 is in theon-state or the off-state. When the even wired OR line OR2 is in theon-state, step 74 is repeated. Further, when the even wired OR line OR2is in the off-state, the routine proceeds to step 75 only in a casewhere the even wired OR line OR2 was determined as in the on-state inthe previous routine. At step 75, the servo controller SC determinesthat the current state is a state to be synchronized, and sets asynchronization point of a number which is the same as the count valueof the synchronization waiting counter. Then, the routine returns tostep 72.

As described above, according to this embodiment, although the driverswhose number is the same as that of the screws are prepared, thestep-by-step screw tightening operations (torque increase operations)can be performed in a short time while preventing inclinations of theclamp plate 25 and the magnetic disks 21, because the start timings ofthe seating operations and the torque increase operations after thesynchronizations of the drivers in the respective pairs (or therespective drivers) have differences.

Further, the torque increase operations are not performed simultaneouslyfor all the screws SR, a turning force acting on the clamp plate 25 andthe magnetic disks 21 is reduced, and therefore the screw tightening ispossible only with the right-handed screws (or the left-handed screws).

Moreover, the setting of the wait time at each torque increase stepenables not only provision of a hold time after reaching the finaltarget torque, but also provision of a hold time even during torqueincrease. Therefore, after the increased torque is sufficientlystabilized at each torque increase step, the following torque increasestep can be performed. With this operation, the clamp plate 25 and thelike can be more certainly prevented from being inclined.

Further, as shown by (a) to (c) in FIG. 4, since the torque increasecommand values (motor voltage command values) are set to be straightlines with limited inclinations, the clamp plate 25 and the like can bemore certainly prevented from being inclined.

Further, in this embodiment, a synchronization circuit can be formed byonly connecting each driver to the two wired OR lines, i.e., withoutproviding a controller superior to the servo controller SC for thesynchronization control, and thus any number of drivers can be selected.Moreover, only providing the two wired OR lines enables synchronizationof many drivers by inverting the respective states of the two wired ORlines at a timing when entering the synchronization waiting state andswitching a wired OR line used for the synchronization determinationbetween the two wired OR lines at the odd numberth synchronization pointand the even numberth synchronization point.

Accordingly, the synchronization circuit can be easily formed at lowcost. Additionally, since a complex determination process is notrequired for the synchronization control, the synchronizationdetermination process can be performed at high speed.

Embodiment 2

FIG. 8 shows a control procedure and operation timings of the screwtightening operations by a screw tightening system that is Embodiment 2of the present invention. This embodiment shows an example of the casein which five screws are tightened with respect to a workpiece such asthe clamp plate 25 or the like by the first to fifth drivers D1 to D5(hereinafter called the drivers 1 to 5) among all the drivers D1 to D6described in Embodiment 1. Constituent components in this embodimentidentical to those in Embodiment 1 are denoted by the same referencenumerals as those in Embodiment 1.

Embodiment 1 described the case in which the start timings of theseating operations and the torque increase operations of the respectivedrivers after the synchronization had differences. However, thisembodiment will describe a case where the seating operations and thetorque increase operations of all the drivers after synchronization aresimultaneously started.

In FIG. 8, (a) to (e) show the operating states of the respectivedrivers and the output states of the even and odd lines in the servocontrollers SC provided to the respective drivers. Moreover, in FIG. 8,(f) shows the states of the even wired OR line OR2 and the odd wired ORline OR1, and (g) shows the state of all the drivers.

Since the negative logic is used in this embodiment as well, a highersignal level corresponds to an off-state (an inactive or H level), and alower signal level corresponds to an on-state (an active or L level).

When a start-up waiting signal from the main controller MC istransmitted to each driver (servo controller SC), each driver enter awaiting state for a screw tightening start command from the maincontroller MC. In this screw tightening start command waiting state, dueto the initialization operations which will be described later, the evenline outputs of all the drivers 1 to 5 are in the off-state and the oddline outputs thereof are in the on-state. With this setting, the evenwired OR line OR2 is in the off-state, and the odd wired OR line OR1 isin the on-state.

Further, each driver (the calculating unit CAL provided to the servocontroller SC) has a counter function of counting the number of times ofsynchronization waiting states. The synchronization waiting counter isset to 0 by an initialization operation which will be described later.The main controller MC may have a synchronization waiting counterfunction, and may receive information on a count value of thesynchronization waiting counter through communication from each driver.

Before waiting for the start command or during waiting for the startcommand, the settings of the screws SR for each driver and the screwholes formed in the workpiece are performed.

When the start command is transmitted from the main controller MC toeach driver, and each driver receives the command, each driver causesthe synchronization waiting counter to increment by one from 0. Further,each driver switches the even line output from the off-state into theon-state, and switches the odd line output from the on-state into theoff-state. FIG. 8 shows a situation in which time differences intransmission of the start command from the main controller MC,variations in the operation characteristics of the respective driversand the like result in time differences in the terminations of the startcommand waiting states of the respective drivers.

When one of the drivers 1 to 5 terminates the start command waitingstate, and the even line output of the driver comes into the on-state,the odd wired OR line OR1 is still in the on-state, and on the otherhand, the even wired OR line OR2 is switched from the off-state into theon-state.

When the start command waiting states of all the drivers 1 to 5 arecompleted, the even wired OR lines OR2 are still in the on-state, andthe odd wired OR lines OR1 are switched from the on-state into theoff-state.

Each driver sets a point in time when the odd wired OR line OR1 isswitched from the on-state into the off-state to an even numberthsynchronization point (where this is a synchronization point 1).

Then, immediately after setting the synchronization point 1, each driverrotates the motor M to tighten the screw until it seats on the clampplate 25 (i.e., the each driver performs the seating operation).

A driver which has detected the seating of the screws by a method whichis the same as that described in Embodiment 1 enters a waiting state forthe following even numberth synchronization point 2. At this time, thedriver causes the synchronization waiting counter to increment by onefrom 1 to 2. Further, the driver switches the even line output from theon-state into the off-state, and switches the odd line output from theoff-state into the on-state.

In accordance with a seating detection of one of the drivers (i.e., theswitching of the even line output from the on-state into the off-stateand the switching of the odd line output from the off-state into theon-state), the even wired OR line OR2 is still in the on-state, and onthe other hand, the odd wired OR line OR1 is switched from the off-stateinto the on-state. In this synchronization waiting state, each drivermaintains its output torque at the point in time when the seatingoperation is completed.

When all the drivers detect seating, the odd wired OR line OR1 is stillin the on-state, and on the other hand, the even wired OR line OR2 isswitched from the on-state into the off-state.

Each driver sets the synchronization point 2 in accordance with theswitching of the even wired OR line OR2 from the on-state into theoff-state.

Each driver which has set the synchronization point 2 immediately startsthe torque increase operation. A driver whose output torque reaches thefirst target torque (T1) enters a waiting state for the following oddnumberth synchronization point 3. At this time, that driver causes thesynchronization waiting counter to increment by one from 2 to 3.Further, the driver switches the even line output from the off-stateinto the on-state, and switches the odd line output from the on-stateinto the off-state.

In accordance with the completion of the torque increase operation up tothe first target torque in one of the drivers (i.e., the switching ofthe even line output from the off-state into the on-state and theswitching of the odd line output from the on-state into the off-state),the even wired OR line OR2 is switched from the off-state into theon-state. On the other hand, the odd wired OR line OR1 is still in theon-state. In this synchronization waiting state, the driver maintainsthe increased output torque (the first target torque).

In accordance with the completion of the torque increase operations upto the first target torque in all the drivers, the even wired OR lineOR2 is still in the on-state, and on the other hand, the odd wired ORline OR1 is switched from the on-state into the off-state.

Each driver sets the synchronization point 3 in accordance with theswitching of the odd wired OR line OR1 from the on-state into theoff-state.

Each driver which has set the synchronization point 3 immediately startsa torque increase operation up to the second target torque (T2).

A driver whose output torque reaches the second target torque enters awaiting state for the following even numberth synchronization point 4.At this time, that driver causes the synchronization waiting counter toincrement by one from 3 to 4. Further, the driver switches the even lineoutput from the on-state into the off-state, and switches the odd lineoutput from the off-state into the on-state.

In accordance with the completion of the torque increase operation inone of the drivers (i.e., the switching of the even line output from theon-state into the off-state and the switching of the odd line outputfrom the off-state into the on-state), the even wired OR line OR2 isstill in the on-state, and on the other hand, the odd wired OR line OR1is switched from the off-state into the on-state. In thissynchronization waiting state, the driver maintains the increased outputtorque (the second target torque).

In accordance with the completion of the torque increase operations upto the second target torque in all the drivers, the odd wired OR lineOR1 is still in the on-state, and on the other hand, the even wired ORline OR2 is switched from the on-state into the off-state.

Each driver sets the synchronization point 4 in accordance with theswitching of the even wired OR line OR2 from the on-state into theoff-state.

Each driver which has set the synchronization point 4 immediately startsthe torque increase operation. A driver whose output torque reaches thefinal target torque enters a waiting state for the following oddnumberth synchronization point 5. At this time, that driver causes thesynchronization waiting counter to increment by one from 4 to 5.Further, the driver switches the even line output from the off-stateinto the on-state, and switches the odd line output from the on-stateinto the off-state.

In accordance with the completion of the torque increase operation up tothe final target torque in one of the drivers (i.e., the switching ofthe even line output from the off-state into the on-state and theswitching of the odd line output from the on-state into the off-state),the even wired OR line OR2 is switched from the off-state into theon-state. On the other hand, the odd wired OR line OR1 is still in theon-state. In this synchronization waiting state, the driver maintainsthe increased output torque (the final target torque).

In accordance with the completion of the torque increase operations upto the final target torque in all the drivers, the even wired OR lineOR2 is still in the on-state, and on the other hand, the odd wired ORline OR1 is switched from the on-state into the off-state.

Each driver sets the synchronization point 5 in accordance with theswitching of the odd wired OR line OR1 from the on-state into theoff-state.

Each driver which has set the synchronization point 5 resets the countvalue of the synchronization waiting counters to 0. Moreover, eachdriver switches the even line output from the off-state into theon-state, and switches the odd line output from the on-state into theoff-state. With this switching, the even wired OR line OR2 is switchedfrom the on-state into the off-state, and the odd wired OR line OR1 isswitched from the off-state into the on-state. This operation is theaforementioned initialization operation. Thus, a series of the screwtightening operations are completed.

In this embodiment, the initialization operation is performed inaccordance with the screw tightening operation is completed. However,the initialization operation may be performed during the start commandwaiting state.

Further, computer programs for controlling the operations relating tothe synchronization in this embodiment are the same as those describedby using FIGS. 7A to 7C in Embodiment 1.

According to this embodiment, a synchronization circuit can be formed byonly connecting each driver to the two wired OR lines, and thus anynumber of drivers can be selected. Moreover, only providing the twowired OR lines enables synchronization of many drivers by inverting therespective states of the two wired OR lines at a timing when enteringthe synchronization waiting state and switching a wired OR line used forthe synchronization determination between the two wired OR lines at theodd numberth synchronization point and the even numberth synchronizationpoint. Accordingly, the synchronization circuit can be easily formed atlow cost. Additionally, since a complex determination process is notrequired for the synchronization control, the synchronizationdetermination process can be performed at high speed.

Embodiments 1 and 2 described the case where the odd and even wired ORlines are singularly provided. However, at least one of the odd and evenwired OR lines may be plurally provided. In this case, the plural wiredOR lines may be alternately used one by one in accordance with that thesynchronization point is what odd or even numberth synchronizationpoint.

Further, a wired OR line other than the odd and even wired OR lines maybe added in order to inform all the drivers of a detection of problem inone of the drivers.

Moreover, Embodiments 1 and 2 described the case where seven or fivesynchronization points are set. However, the number of synchronizationpoints is not limited thereto in the present invention.

Embodiment 3

Embodiments 1 and 2 described the case where the synchronization controlfor the screw tightening drivers is performed by using the odd and evenwired OR lines. However, the same synchronization control can be appliedto a motor-driven apparatus other than the screw tightening drivers.

FIG. 9 illustrates a synchronization control system for performingposition control of an object (a robot arm, a positioning table or thelike) P in directions of four axes (X-, Y-, Z-, and θ-axes) which isEmbodiment 3 of the present invention. Constituent components in thisembodiment shown in FIG. 9 identical to those in Embodiment 1 aredenoted by the same reference numerals as those in Embodiment 1. In thisembodiment, synchronization control of motors MX, MY, MZ, and MO fordrive in the directions of the X, Y, Z, and θ-axes in place of the screwtightening drivers in Embodiment 1 is performed.

FIG. 10 shows a control procedure and operation timings of thisembodiment. This embodiment will describe, in the same way as inEmbodiment 2, a case where operations of all the motors aftersynchronization are simultaneously started.

In FIG. 10, (a) to (d) show the operating states of the motors for therespective axes and the output states of the even and odd lines in servocontrollers SC provided for the respective motors. In the followingdescription, the servo controller SC and the motor for each axis areinclusively called the servo controller SC.

Moreover, in FIG. 10, (e) shows the states of the even wired OR line OR2and the odd wired OR line OR1. Further, in FIG. 10, (f) shows the stateof all the servo controllers SC.

Since the negative logic is used in this embodiment as well, a highersignal level corresponds to an off-state (an inactive or H level), and alower signal level corresponds to an on-state (an active or L level).

When a start-up waiting signal from the main controller MC istransmitted to each servo controller SC, each servo controller SC entersa waiting state for a start command for a continuous positioningoperation from the main controller MC. In this start command waitingstate, due to an initialization operation which will be described later,the even line outputs of all the servo controllers SC are in theoff-state and the odd line outputs thereof are in the on-state. Withthis setting, the even wired OR line OR2 is in the off-state, and theodd wired OR line OR1 is in the on-state.

Further, each servo controller SC has a counter function of counting thenumber of times of synchronization waiting states. The synchronizationwaiting counter is set to 0 by the initialization operation which willbe described later. The main controller MC may have a synchronizationwaiting counter function, and may receive information on a count valueof the synchronization waiting counter through communication from eachservo controller SC.

When the start command is transmitted from the main controller MC toeach servo controller SC, and each servo controller SC receives thecommand, each servo controller SC causes the synchronization waitingcounter to increment by one from 0. Further, each servo controller SCswitches the even line output into the on-state, and switches the oddline output into the off-state. FIG. 10 shows a situation in which timedifferences in transmission of the start command from the maincontroller MC, variations in the operation characteristics of therespective servo controllers SC and the like result in time differencesin the terminations of the start command waiting states of therespective servo controllers SC.

When one of the servo controllers SC terminates the start commandwaiting state, and the even line output of the servo controller SC comesinto the on-state, the odd wired OR line OR1 is still in the on-state,and on the other hand, the even wired OR line OR2 is switched from theoff-state into the on-state.

When the start command waiting states of all the servo controllers SCare completed, the even wired OR line OR2 is still in the on-state, andthe odd wired OR line OR1 is switched from the on-state into theoff-state.

Each servo controller SC sets a point in time when the odd wired OR lineOR1 is switched from the on-state into the off-state to an even numberthsynchronization point (where this is a synchronization point 1).

Then, immediately after setting the synchronization point 1, each servocontroller SC rotates the motor to start driving the object P to a firstcoordinate position (x1, y1, z1, and θ). FIG. 10 shows that differencesin the driving amounts of the respective axes result in the timedifferences up to the driving termination.

The servo controller SC which has completed the driving of the object Pto the first coordinate position enters a waiting state for thefollowing even numberth synchronization point 2. At this time, thatservo controller SC causes the synchronization waiting counter toincrement by one from 1 to 2. Moreover, the servo controller SC switchesthe even line output from the on-state into the off-state, and switchesthe odd line output from the off-state into the on-state.

In accordance with the termination of the driving by one of the servocontrollers SC, the even wired OR line OR2 is still in the on-state, andon the other hand, the odd wired OR line OR1 is switched from theoff-state into the on-state.

When the driving of the object P to the first coordinate position iscompleted in all the servo controllers SC, the odd wired OR line OR1 isstill in the on-state, and on the other hand, the even wired OR line OR2is switched from the on-state into the off-state.

Each servo controller SC sets the synchronization point 2 in accordancewith the switching of the even wired OR line OR2 from the on-state intothe off-state. Then, each servo controller SC starts driving the objectP to a second coordinate position (x2, y2, z1, and θ1). Here, a case isshown in which the object P is driven only in the directions of theX-axis and the Y-axis, and is fixed in the directions of the Z-axis andthe θ-axis.

The servo controller SC which has completed the driving of the object Pto the second coordinate position enters a waiting state for thefollowing odd number synchronization point 3. The servo controllers SCfor the directions of the Z-axis and the θ-axis in which the object P isfixed enter a waiting state for the synchronization point 3 after apredetermined time has elapsed from the synchronization point 2. Theservo controller SC in the state waiting for the synchronization point 3causes the synchronization waiting counter to increment by one from 2 to3. Further, the servo controller SC switches the even line output fromthe off-state into the on-state, and switches the odd line output fromthe on-state into the off-state.

When any one of the servo controllers SC comes into the synchronizationwaiting state, the even wired OR line OR2 is switched from the off-stateinto the on-state. On the other hand, the odd wired OR line OR1 is stillin the on-state.

When all the servo controllers SC come into the synchronization waitingstate, the even wired OR line OR2 is still in the on-state, and on theother hand, the odd wired OR line OR1 is switched from the on-state intothe off-state.

Each servo controller SC sets the synchronization point 3 in accordancewith the switching of the odd wired OR line OR1 from the on-state intothe off-state. Then, each servo controller SC starts driving the objectP to a third coordinate position (x3, y2, z1, and θ3). Here, a case isshown in which the object P is driven only in the directions of theX-axis and the θ-axis, and is fixed in the directions of the Y-axis andthe Z-axis.

The servo controller SC which has completed the driving of the object Pto the third coordinate position enters a waiting state for thefollowing even numberth synchronization point 4. The servo controllersSC for the directions of the Y-axis and the Z-axis in which the object Pis fixed enter a waiting state for the synchronization point 4 after apredetermined time has elapsed from the synchronization point 3. Theservo controller SC in the state waiting for the synchronization point 4causes the synchronization waiting counter to increment by one from 3 to4. Moreover, the servo controller SC switches the even line output fromthe on-state into the off-state, and switches the odd line output fromthe off-state into the on-state.

When any one of the servo controllers SC comes into the synchronizationwaiting state, the even wired OR line OR2 is still in the on-state, andon the other hand, the odd wired OR line OR1 is switched from theoff-state into the on-state. When all the servo controllers SC come intothe synchronization waiting state, the odd wired OR line OR1 is still inthe on-state, and on the other hand, the even wired OR line OR2 isswitched from the on-state into the off-state.

Each servo controller SC sets the synchronization point 4 in accordancewith the switching of the even wired OR line OR2 from the on-state intothe off-state. Then, each servo controller SC starts driving the objectP to a final coordinate position (x3, y3, z4, and θ3). Here, a case isshown in which the object P is driven only in the direction of theZ-axis, and is fixed in the directions of the X-axis, the Y-axis, andthe θ-axis.

The servo controller SC which has completed the driving of the object Pto the final coordinate position enters a waiting state for thefollowing odd numberth synchronization point 5. The servo controllers SCfor the directions of the X-axis, the Y-axis, and the θ-axis in whichthe object P is fixed enter a waiting state for the synchronizationpoint 5 after a predetermined time has elapsed from the synchronizationpoint 4. The servo controller SC in the state waiting for thesynchronization point 5 causes the synchronization waiting counter toincrement by one from 4 to 5. Further, the servo controller SC switchesthe even line output from the off-state into the on-state, and switchesthe odd line output from the on-state into the off-state.

When any one of the servo controllers SC comes into the synchronizationwaiting state, the even wired OR line OR2 is switched from the off-stateinto the on-state. On the other hand, the odd wired OR line OR1 is stillin the on-state.

When all the servo controllers SC come into the synchronization waitingstate, the even wired OR line OR2 is still in the on-state, and on theother hand, the odd wired OR line OR1 switched from the on-state intothe off-state.

Each servo controller SC sets the synchronization point 5 in accordancewith the switching of the odd wired OR line OR1 from the on-state intothe off-state. The main controller MC which has detected the setting ofthe synchronization point 5 transmits a continuous movement terminationcommand to each servo controller SC.

Each servo controller SC received the termination command resets thecount value of the synchronization waiting counter to 0. Further, eachservo controller SC switches the even line output from the on-state intothe off-state, and switches the odd line output from the off-state intothe on-state. With this switching, the even wired OR line OR2 isswitched from the on-state into the off-state, and the odd wired OR lineOR1 is switched from the off-state into the on-state. This operation isthe aforementioned initialization operation. In this way, a series ofcontinuous positioning operations are completed.

In this embodiment, the initialization operation is performed inaccordance with the completion of the continuous positioning operation.However, the initialization operation may be performed during the startcommand waiting state.

Further, computer programs for controlling the operations relating tothe synchronization in this embodiment are the same as those describedby using FIGS. 7A to 7C in Embodiment 1.

According to this embodiment, a synchronization circuit can be formed byonly connecting each servo controller SC to the two wired OR lines, andthus any number of driving axes can be selected. Moreover, onlyproviding the two wired OR lines enables synchronization of many servocontrollers SC by inverting the respective states of the two wired ORlines at a timing when entering the synchronization waiting state andswitching a wired OR line used for the synchronization determinationbetween the two wired OR lines at the odd numberth synchronization pointand the even numberth synchronization point. Accordingly, thesynchronization circuit can be easily formed at low cost. Additionally,since a complex determination process is not required for thesynchronization control, the synchronization determination process canbe performed at high speed.

This embodiment described the case where the odd and even wired OR linesare singularly provided. However, at least one of the odd and even wiredOR lines may be plurally provided. In this case, the plural wired ORlines may be alternately used one by one in accordance with that thesynchronization point is what odd or even numberth synchronizationpoint.

Further, a wired OR line other than the odd and even wired OR lines maybe added in order to inform all the servo controllers SC (driving axes)of a detection of problem in one of the servo controllers SC.

Moreover, this embodiment described the case where the fivesynchronization points are set. However, the number of synchronizationpoints is not limited thereto in the present invention.

Embodiment 4

In order to prevent the inclination of the workpiece by the step-by-steptightening torque increase control as described in Embodiments 1 and 2,each of actual screw tightening drivers must precisely generate anoutput torque (tightening torque) corresponding to a motor voltage ormotor current command value (torque command value) regardless of itsrotational angle.

However, cogging torque of a motor serving as a driving source of thescrew tightening driver (torque fluctuations due to unevenness ofpermeability of a core of the motor or due to dimension errors andfabrication errors of parts constituting the motor) appears as atightening torque fluctuation of the screw tightening driver in manycases. Additionally, in some cases, the magnitude of the torquefluctuation in the motor M varies in accordance with the level of thetorque command value (a motor applied voltage or a motor appliedcurrent) due to winding unevenness of a motor winding or the like.

Therefore, it is necessary to measure actual tightening torque of thescrew tightening driver for the torque command value at every rotationalangle, and to correct the torque command value provided to the driver soas to suppress a fluctuation in tightening torque according to therotational angle.

This embodiment will describe a torque measurement apparatus capable ofautomatically measuring the output torque of the screw tightening driverat every predetermined rotational angle.

FIGS. 11 and 12 respectively show an external view and a block diagramof the torque measurement apparatus of this embodiment. In thesedrawings, reference numeral 10 denotes a base. A stepping motor 11 and arotation mechanism 12 driven by the motor 11 are attached to the base10.

The rotation mechanism 12 includes at its upper end a rotary table 13supported by a shaft 18 shown in FIG. 12. The rotation mechanism 12includes at its lower end a pulley 12 a to input rotation, and aHarmonic Drive (Registered Trademark) (not shown) that reduces the speedof the rotation input through the pulley 12 a to transmit the rotationto the rotary table 13.

A belt 11 b is wound over between the pulley 12 a and a pulley 11 aattached to the output shaft of the motor 11. Therefore, when the motor11 rotates, the rotary table 13 is rotated around the shaft 18 through aspeed reduction by the belt 11 b and the pulleys 11 a and 11 b servingas a first speed reduction mechanism and a speed reduction by theharmonic drive serving as a second speed reduction mechanism. A speedreduction function greater than the pulley belt mechanism of theharmonic drive can provide finer rotational angle resolution of therotary table 13 than a step angle after the speed reduction by thepulley belt mechanism. As the first speed reduction mechanism, a gearingsystem or a roller mechanism other than the pulley belt mechanismdescribed above may be used. However, a mechanism with extremely-littlebacklash or slippage should be selected as the first speed reductionmechanism.

Reference numeral 17 denotes a rotational angle sensor fixed to the base10, which detects a rotational angle of the rotary table 13. Aring-shaped pulse plate is attached so as to face the upper surface ofthe rotational angle sensor 17 on the lower surface of the rotary table13. The rotational angle sensor 17 irradiates light onto the pulse plateand receives light in a pulsed form reflected on the pulse plate tooutput a pulse signal. As the rotational angle sensor 17, a sensor in adetection method other than such an optical detection method sensor maybe used. The output signal from the rotational angle sensor 17 is inputto a personal computer 30 which will be described later.

Reference symbol D denotes a screw tightening driver serving as ameasuring object, which is fixed to a lifting table 10 b of an liftingmechanism 10 a provided to the base 10.

A torque sensor 15 is fixed to the rotary table 13 via a holding member14. A bit B of the screw tightening driver D is connected to the torquesensor 15 via a coupling 16. The torque sensor 15 outputs an electricalsignal corresponding to the torque received from the bit B. There are awide variety of torque sensors of a strain gauge method, amagnetostrictive effect method, a phase difference detection method, amechanical reactive force method, a contact type, a noncontact type andthe like. However, a type of the torque sensor used in this embodimentand the present invention may be any one of them.

Although not shown in FIG. 11, as shown in the parentheses in FIG. 12, aload cell 19 serving as an axial force sensor may be provided above thetorque sensor 15 via the coupling 16. The load cell 19 detects an axialforce (screw axial force) generated in a screw SR tightened by thedriver D. With respect to the load cell 19 as well, any type thereof maybe used as is the case with the torque sensor 15.

Reference numerals 33 and 34 denote indicators which respectivelytransfer detection signals from the torque sensor 15 and the load cell19 to the personal computer 30, and convert the detection signals intonumeric signals to indicate a torque value and an axial force value asnumeric values thereon.

As shown in FIG. 12, the measurement apparatus and the screw tighteningdriver D are driven by a controller including the personal computer 30,a motor control unit 31, and a screw tightening control board 32, toperform a measurement operation.

The motor control unit 31 controls the rotation of the motor 11 inaccordance with a command from the personal computer 30.

Further, the screw tightening control board 32 is identical to that usedin the motor control unit C2 of the servo controller SC described inEmbodiments 1 and 2.

As in embodiments which will be described later, a function ofcorrecting the torque command value on the basis of the torquecharacteristic (torque fluctuation) measured by the measurementapparatus of this embodiment is added to the motor control unit C2actually used in the screw tightening system. However, in a case inwhich a torque correction effect obtained by the function is confirmed,the screw tightening control board 32 to which the function is added isused.

Next, description of the measurement operation by the torque measurementapparatus formed as described above will be made by using FIG. 13. FIG.13 is an operational flowchart of the personal computer 30 that controlsthe torque measurement apparatus. Further, the measurement operation ina case in which the load cell 19 is provided in addition to the torquesensor 15 will be described.

When the measurement operation is started, the personal computer 30drives the motor 11 via the motor control unit 31 first to set therotary table 13 to a position of the original point of θ=0 at step 120.At this time, a rotational angle counter (not shown) provided inside thepersonal computer 30 is reset to 0.

Next, at step 121, the personal computer 30 confirms whether or not thescrew SR set in advance is in a seating state on the load cell 19. Theseating detection method described in Embodiment 1 may be used for thisseating confirmation.

Next, at step 122, the personal computer 30 outputs a torque command tothe screw tightening control board 32. The torque command can beappropriately selected within a range used for tightening the screw SRin the actual screw tightening system. For example, a torque commandcorresponding to the final target torque described in Embodiments 1 and2 may be selected.

The torque command is fixed during at least one rotation (360° rotation)of the rotary table 13. The screw tightening control board 32 thatreceived the torque command applies a voltage corresponding to thetorque command to the motor M of the driver D to provide a turning force(tightening torque) to the bit B.

Next, at step 123, the personal computer 30 records a screw axial forcevalue indicated by a detection signal from the load cell 19 and a torquevalue indicated by a detection signal from the torque sensor 15 togetherwith a count value of the rotational angle counter in a memory providedin the personal computer 30.

In a case in which the measurement at the original point position isperformed, the personal computer 30 records the values as, for example,“0.00°: SF, TS”, where SF represents the screw axial force and TSrepresents the tightening torque.

Next, at step 124, the personal computer 30 determines whether or notthe count value of the rotational angle counter has reached ameasurement termination angle (for example, 360°). When the count valuehas not reach the measurement termination angle, the personal computer30 proceeds to step 125 to output a command to the motor control unit 31for rotating the rotary table 13 (i.e., the torque sensor 15 and the bitB coupled therewith) by a predetermined rotational angle. Thepredetermined rotational angle can be set to any angle in advance by ameasurer.

Then, the personal computer 30 returns to step 122 to perform themeasurement and recording of the screw axial force and the screwtightening torque at an angle after the rotation. In this way, thepersonal computer 30 repeats to rotate the rotary table 13 and tomeasure and record the screw axial force and the tightening torque untilthe count value of the rotational angle counter reaches the measurementtermination angle. When the count value reaches the measurementtermination angle, the personal computer 30 proceeds to step 126.

At step 126, the personal computer 30 tabulates the results of theseries of measurements repeated from the original point position todisplay them in a graph form or the like on a monitor (not shown). Then,the personal computer 30 completes the operations for measuringfluctuations in screw axial force and tightening torque during at leastone rotation of the driver D.

The description was made of the case in which the measurement of thescrew axial force and the tightening torque for one torque command isperformed at every rotational angle. However, as shown at step 128 inFIG. 13, the step 122 and the step 123 may be repeatedly performed whileincreasing the torque value step by step at every rotational angle (forexample, while step by step increasing the torque value from the firsttarget torque to the final target torque as described in Embodiment 1).With this operation, in a case in which the magnitude of the torquefluctuation in the motor M varies in accordance with the level of thetorque command value (the motor applied voltage or the motor appliedcurrent), the torque fluctuation in the driver D at each command valuecan be measured.

FIG. 14 illustrates a measurement result of a fluctuation in tighteningtorque in one rotation, which is obtained by the torque measurementapparatus. FIG. 14 shows the measured tightening torque in a case inwhich the rotary table 13 is rotated by each angle corresponding to360°/2047 (about 0.176°). Reference symbol TI in the drawing denotes thetorque command value.

According to this embodiment, even in a case in which one rotation ofthe driver D is divided into extremely many rotational angles, accuratemeasurement and recording of the tightening torque and the screw axialforce at every angle are automatically performed, and the tabulation anddisplay of the results thereof are further automatically performed.Therefore, the measurement and display of the results thereof can beperformed in a shorter time with significantly finer resolution andhigher accuracy as compared with a conventional measurement method inwhich the setting is manually performed at every rotational angle.

Further, providing the load cell 19 along with the torque sensor 15enables the measurements of the tightening torque and the screw axialforce generated by the tightening torque simultaneously. A relationshipbetween a tightening torque applied to a screw and an axial forcegenerated in the screw can be estimated by calculation. However, themeasurement of a screw axial force actually generated can be effectivelyused for more precisely performing the setting and management of thetightening torque in the screw tightening system.

This embodiment described the case where the tightening torque of thescrew tightening driver is measured by the torque measurement apparatus.However, the torque measurement apparatus of the present invention canbe used for measuring an output torque of a motor-driven apparatus usinga motor as a driving source, which is other than the screw tighteningdriver, and an output torque of a simple motor.

Embodiment 5

As described at the beginning of Embodiment 4, in order to prevent theinclination of the workpiece by performing the step-by-step tighteningtorque increase control as in Embodiments and 2, the actual screwtightening driver must precisely generate the output torquecorresponding to the motor voltage command value (torque command value)regardless of its rotational angle. However, the cogging torque of themotor serving as the driving source of the screw tightening driver(torque fluctuations due to unevenness of permeability of the core, anddimension errors and fabrication errors of parts constituting the motor)appears as the tightening torque fluctuation of the screw tighteningdriver in many cases. Moreover, in some cases, the magnitude of thetorque fluctuation in the motor M varies in accordance with the level ofthe torque command value (the motor applied voltage or the motor appliedcurrent) due to the winding unevenness of the motor winding or the like.

Then, this embodiment will describe a screw tightening apparatus inwhich the tightening torque fluctuations with respect to the torquecommand values at a plurality of levels are measured by using the torquemeasurement apparatus shown in Embodiment 4, and the tightening torquefluctuation at each torque level can be corrected at every extremelyfine rotational angle.

FIG. 15 illustrates the configuration of part of the screw tighteningsystem which is Embodiment 5 of the present invention.

Reference numeral 81 denotes a torque increase control unit provided tothe servo controller SC. In the torque increase control unit 81, asdescribed in Embodiment 1, a map of a torque command value T(t) which iscommand data transmitted from the main controller MC is stored in amemory thereof. FIG. 15 shows the torque command value map in which atorque value is continuously increased. However, in reality, this is amap in which a torque value is increased step-by-step while waiting therespective synchronization points described in Embodiments 1 and 2.

Correction data memories 82, 83, and 84, an interpolation calculationpart 86, an adder 87, a torque control unit 88, and an amplifier A whichwill be described below are provided in the motor control unit C2 (referto FIG. 2) of the servo controller SC.

Torque correction tables serving as correction data groups which will bedescribed later are stored in the correction data memories 82, 83, and84.

A torque correction table H stored in the memory 82 is a correction datatable to correct the torque command value when a high-level torquecommand value TH (for example, a maximum target torque value Tmax inEmbodiments 1 and 2) is input as the torque command value T(t) to theservo controller SC from the torque increase control unit 81.

A method for preparing the torque correction table H will be describedby using FIG. 16A. First, a tightening torque when the torque commandvalue TH is issued to the driver D is measured several times at everypredetermined rotational angle of the driver D by using the torquemeasurement apparatus described in Embodiment 4 (step <which isabbreviated as S in the figure> 201). Typical torque fluctuation data isobtained by averaging the measurement results of the several times(refer to FIG. 14) or by performing polynomial approximation by aleast-square method (step 202). With this operation, torque fluctuationdata from which the effect of noise components other than torquefluctuation components unique to the motor M serving as the drivingsource of the driver D is eliminated can be obtained. The noisecomponents include, for example, a torque fluctuation component due to africtional fluctuation of gears when the driver D includes a reductiongear. The least-square method is a technique for determining acoefficient of a model function with which a square sum of differencesbetween measurement values and model function values is minimized.

Then, a difference between the obtained typical torque fluctuation dataand the torque command value TH is calculated for every rotational angle(step 203). When a value of the difference is a positive value, the samevalue with negative sign is a correction value for that rotationalangle, and when a value of the difference is a negative value, the samevalue with positive sign is a correction value for that rotationalangle. In this way, correction values for all the rotational angles arecalculated, and then the torque correction table H is prepared as atable of the correction values in accordance with the rotational angles(step 204). Then, the prepared torque correction table H is stored inthe correction data memory 82 (step 205).

This torque correction table may be automatically prepared by thepersonal computer 30 shown in Embodiment 4. Further, the torquecorrection table may be prepared by using a method other than the methoddescribed above. For example, the torque correction table may beprepared such that an average torque value between a maximum torquevalue and a minimum torque value obtained on the basis of themeasurement results of the torque fluctuations is calculated, and adifference between the average torque value and a value of thefluctuation data at every rotational angle is determined, and the signof a value of the difference is reversed.

A torque correction table L stored in the memory 83 is a correction datatable to correct the torque command value when a low-level torquecommand value TL (for example, the first target torque value inEmbodiments 1 and 2) is input as the torque command value T(t) to theservo controller SC from the torque increase control unit 81.

Moreover, a torque correction table ML stored in the memory 84 is acorrection data table to correct the torque command value when amiddle-level torque command value TML (for example, a torque valueintermediate between the maximum target torque value Tmax and the firsttarget torque value) is output as the torque command value T(t) from thetorque increase control unit 81. A method for preparing these torquecorrection tables L and ML is the same as that for the torque correctiontable H described above.

In this embodiment, in order to prepare the torque correction tables H,L, and ML for three torque command values, it is necessary to measurethe tightening torques for the three torque command values by the torquemeasurement apparatus described in Embodiment 4.

Examples of the torque correction tables H, L, and ML are shown in FIG.16B. The values of the respective torque correction tables shown in thisdrawing vary to a positive side and a negative side from the borderlineof 0 in accordance with the rotational angle of the driver D. Further,the values of the respective torque correction tables vary so as to beformed into, not line shapes and not sinusoidal waveforms, but complexshapes.

The torque command value T(t) is input from the torque increase controlunit 81 to the interpolation calculation part 86, and a signal from anencoder E (which may be a tachometer generator) for detecting therotational angle of the motor M of the driver D is input thereto.

The interpolation calculation part 86 selects from the three torquecorrection tables H, L, and ML a correction data table for a torquecommand value corresponding to the input torque command value T(t) ortwo correction data tables for two torque command values between whichthe input torque command value T(t) is present. FIG. 15 shows a casewhere the torque correction tables H and ML are selected because theinput torque command value T(t) is present between the torque commandvalues TH and TML.

Then, the interpolation calculation part 86 reads out a correction valuecorresponding to the rotational angle of the driver D detected throughthe encoder E from the selected torque correction table. When theselected torque correction table is a table for the torque command valuecorresponding to the torque command value T(t), the interpolationcalculation part 86 directly outputs the read correction value. Further,when two torque correction tables are selected, and two correctionvalues are read out of these tables, the interpolation calculation part86 determines a correction value for the torque command value T(t) by aninterpolation calculation on the basis of these two correction values(step 206 in FIG. 16A).

FIG. 15 shows an example in which a correction value C for the torquecommand value T(t) is calculated by linear interpolation by using twocorrection values CH(θ) and CML(θ) read out from the torque correctiontables H and ML.

In detail, first, in a case of T(t)>TML, the torque correction tables Hand ML are selected to read out CH(θ) and CML(θ).

Then, in accordance with proportional distribution of CH(θ) and CML(θ),the correction value C is calculated on the basis of:

C={CH(θ)−CML(θ)}/(TH−TML)×(T(t)−TML)+CML(θ).

In a case of T(t)<TML, the torque correction tables ML and L areselected to read out CML(θ) and CL(θ).

Then, in accordance with proportional distribution of CML(θ) and CL(θ),the correction value C is calculated on the basis of:

C={CML(θ)−CL(θ)}/(TML−TL)×(T(t)−TL)+CL(θ).

Even in a case in which T(t) corresponds to one of TH, TML, and TL, thecorrection value may be calculated by applying T(t) to theabove-described linear interpolation formula.

The method for calculating the correction value C is not limited to thelinear interpolation method as described above. An interpolation may beperformed by using, for example, a quadratic or higher-order expressionincluding three points (TL, CL(θ)), (TML, CML(θ)), and (TH, CH(θ)).

Further, when TH is less than the maximum torque command value in thescrew tightening or greater than the minimum torque command value (thefirst target torque value) in the screw tightening, the correction valueC may be determined by, not the interpolation method described above,but an extrapolation method.

Moreover, this embodiment described the case where the torque correctiontables H, L, and ML for the three torque command values are prepared.However, in the present invention, torque correction tables for twotorque command values or four or more torque command values may beprepared. In a case as well where four or more torque correction tablesare prepared, the correction value C may be determined by theinterpolation method or the extrapolation method using the correctiontables for two torque command values between which the input torquecommand value T(t) is present. In this way, preparing many correctiontables enables a favorable reduction of the torque fluctuations evenwhen the nonlinearity is strong in the relationship between the torquecommand value (motor applied voltage) and the output torque.

The correction value C obtained in this way is output form theinterpolation calculation part 86 to be added to the torque commandvalue T(t) input from the torque increase control unit 81 by the adder87 (step 207 in FIG. 16A). Then, a corrected torque command value T′(t)(=T(t)+C) is input to the torque control unit 88.

The torque control unit 88 outputs a voltage corresponding to thecorrected torque command value T′(t) to the amplifier A, and then avoltage amplified by the amplifier A is applied to the motor M. Withthis voltage, the driver D can generate a tightening torquecorresponding to the original torque command value T(t). Thus, thetightening torque fluctuations of the screw tightening driver due to thecogging torque of the motor M, the permeability unevenness of the core,and the dimension errors and fabrication errors of parts constitutingthe motor M can be favorably corrected.

Then, performing such a correction of the torque command value T(t) forevery rotational angle enables reduction of the torque fluctuationsassociated with changes in rotational angle of the driver D, therebymaking it possible to stably generate a tightening torque correspondingto the torque command value T(t).

Moreover, in this embodiment, since the correction value C is optimizedin accordance with the level of the torque command value, the torquefluctuations can be reduced within a wide range of torque levels.

FIG. 17 shows an example (an image view) in a case where the torquefluctuations of the screw tightening driver are corrected by the methoddescribed in this embodiment. In FIG. 17, reference symbols TA, TB, andTC denote arbitrary torque command values, which are in a relationshipof TA>TB>TC.

Reference symbols J in the drawing denote data obtained by averaging orapproximating with the least-square method the measurement data of thetightening torques generated in the actual screw tightening driver forthe torque command values TA, TB, and TC. Further, reference symbols Kin the drawing denote data obtained by averaging or approximating withthe least-square method the measurement data of the tightening torquesgenerated in the screw tightening driver for the torque command valuescorrected by the method described in this embodiment. Both measurementdata are obtained by the torque measurement apparatus of Embodiment 4.

As understood from FIG. 17, a fluctuation amount of the tighteningtorque J before correcting the torque command value increases as thelevel of the torque command value increases. Further, the fluctuatingmanner of the tightening torque J is complex.

In contrast thereto, a fluctuation amount of the tightening torque K forthe corrected torque command value is reduced at any torque level, whichenables stable generation of tightening torques approximate to thetorque command values TA, TB, and TC.

Accordingly, using this embodiment in the screw tightening system inEmbodiments 1 and 2 enables tightening of the screw SR with screwtightening torques certainly corresponding to the torque command values(the first to final target torque values).

This embodiment described the correction of the torque fluctuations ofthe screw tightening driver. However, the present invention can beapplied to not only the screw tightening driver, but also a motor-drivenapparatus using a motor as a driving source and a simple motor whichneed accurate torque control.

Moreover, when not only torque control, but also speed control orposition control is performed with a motor serving as a driving source,the present invention can be used for the purpose of suppressing due toa cogging torque of the motor.

Moreover, the present invention can be applied for the purpose ofperforming precise driving force control for, not only a rotary motorsuch as a brush motor or a brushless motor, but also a linear motorgenerating a rectilinear driving force.

In this embodiment, the correction data memories 82 to 84 in which thecorrection data unique to the driver D are stored are provided in theservo controller SC which is provided as a set (pair) with the driver D.With this configuration, even when it is necessary to replace the driverD and the servo controller SC in the screw tightening system, storingthe correction data unique to the driver D in a driver D and a servocontroller SC which are newly installed enables a prompt response.

Further, the correction data memories 82 to 83 may be provided, not inthe servo controller SC, but integrally to the driver D. This enables aprompt response to a replacement of only the driver D.

Moreover, in the servo controller SC, a memory may be prepared in whicha plurality of correction data tables corresponding to a plurality ofdrivers D identifiable by identification numbers or the like are stored.This enables, when the identification number of a driver D to be used isinput to the interpolation calculation part 86, automatic selection of acorrection data table for the driver D.

Embodiment 6

FIG. 18 illustrates a screw tightening driver (screw tighteningapparatus) that is Embodiment 6 of the present invention. Embodiments 1,2, 4, and 5 described the method for controlling the screw tighteningdriver used for the screw tightening and the method for correcting thetightening torque fluctuations at the time of assembling products suchas hard disk drives.

However, in association with miniaturization of computers and theirperipherals in recent years, further miniaturization of products such ashard disk drives is required. Then, the miniaturization of productsfurther reduces the size of screws used for assembling the products.

This embodiment will describe a screw tightening driver which is notonly used as the screw tightening driver described in Embodiments 1, 2,4, and 5, but which may also have applicability to tightening of furtherminiaturized screws. In the following description, the upper side inFIG. 18 is referred to as an upper side of the screw tightening driver,and the lower side in FIG. 18 is referred to as a lower side of thescrew tightening driver.

In FIG. 18, reference symbol D denotes a driver, and reference numeral91 denotes a gear box. The motor M is fixed to the upper surface of thegear box 91. An output gear 91 a integrally attached to the output shaftof the motor M protrudes toward the inside of the gear box 91.

A double gear 91 b whose large-diameter gear portion engages with theoutput gear 91 a, and an idler gear 91 c which engages with asmall-diameter gear portion of the double gear 91 b are disposed insideof the gear box 91.

Reference numeral 92 a denotes an external cylindrical member forming amain body portion of a bit driving unit which is also shown withreference symbol BD in FIG. 1. An output shaft 93 extending verticallyis disposed inside of the external cylindrical member 92 a.

The output shaft 93 includes a shaft portion 93 b extending upward anddownward, and a driven gear 93 a formed between (at a verticallyintermediate position of) the shaft portion 93 b. The driven gear 93 aincludes gear teeth which extend vertically and engage with the idlergear 91 c. This embodiment uses the output shaft 93 in which the shaftportion 93 b and the driven gear 93 a are integrally formed. However,the driven gear 93 a and the shaft portion 93 b may be separatelymanufactured and then the shaft portion 93 b may be pressed into thedriven gear 93 a to be integrated therewith.

The shaft portion 93 b of the output shaft 93 are rotatably supported atits upper and lower parts by two ball bearings 94 a and 94 b fixed tothe inner circumference of the connecting portion with the externalcylindrical member 92 a in the gear box 91. A bit B for the screwtightening is connected so as to be integrally rotatable and detachableto the lower end of the shaft portion 93 b.

A vertical length (thickness) of the driven gear 93 a is set to begreater than that of the idler gear 91 c. The reason for this is that,in order to maintain the engagement between the bit B and a recess of ascrew at the time of screw tightening, the bit B and the output shaft 93must be vertically movable as shown by an arrow V in the drawing withrespect to the external cylindrical member 92 a and the gear box 91while maintaining the engagement between the driven gear 93 a and theidler gear 91 c.

Namely, the reason for this is that turning force transmission from themotor M to the output shaft 93 is made possible regardless of a verticalmovement of the output shaft 93. In detail, the thickness of the drivengear 93 a is set to be equal to or greater than a length of a screw tobe tightened plus the thickness of the idler gear 91 c.

Further, a sleeve 98 surrounding the outer circumference of the bit B isfitted to be vertically movable in the lower portion of the externalcylindrical member 92 a. The sleeve 98 is biased downward by a sleevepresser spring 92 d disposed between an upper end of the sleeve 98 and aflange portion of the external cylindrical member 92 a supporting thelower ball bearing 94 b at the inner circumferential portion of theexternal cylindrical member 92 a.

Further, a negative pressure connection member 98 a is provided in alower side wall of the sleeve 98. A hose from a vacuum pump (not shown)is connected to the negative pressure connection member 98 a. Making anegative pressure state in the sleeve 98 in a state in which a head ofthe screw is housed in the lower end portion of the sleeve 98 enablesabsorption of the screw and engagement of the bit B with the recess ofthe screw.

As described above, in this embodiment, the driven gear 93 a isintegrally formed with the output shaft 93 or pressed into the outputshaft 93 to be integrated therewith. This is for the following reason.In order to configure the driven gear 93 a and the output shaft 93 so asto be relatively movable by spline coupling, unless the shaft portion 93b has a certain measure of diameter, it is difficult to form a keygroove for the spline coupling on the shaft portion 93 b. Even if thekey groove can be formed, it is difficult to form it into a highlyaccurate shape for suppressing eccentric rotation and a torquefluctuation. Additionally, if the diameter of the shaft portion 93 b issmall, even when the shaft portion 93 b is spline-coupled to the drivengear 93 a, there is a high possibility that transmission of asufficiently high torque from the driven gear 93 a to the shaft portion93 b cannot be performed.

According to this embodiment in which the driven gear 93 a is integratedwith the output shaft 93 so as to cause the driven gear 93 a to beslidable with respect to the idler gear 91 c, even if the diameter ofthe shaft portion 93 b is small, manufacturing and accurizing of thedriver are easy, and transmission of a sufficiently high torque ispossible.

Since the diameter of the bit B is small in the driver used fortightening fine screws and a pitch between the screws to be tightenedare narrow, it is necessary to make the diameter of the driver D (inparticular, the diameter of the external cylindrical member 92 a) smallby making the diameter of the output shaft 93 (shaft portion 93 b)small. According to the configuration of this embodiment, uponsatisfaction of such requirements, fine screws can be tightened byrotation of the bit with little eccentricity and torque fluctuation at adesired torque.

On the other hand, a spring receiving member 96 is attached to a partabove the driven gear 93 a in the shaft portion 93 b via a bearing 95,as shown in detail in FIG. 19.

The spring receiving member 96 includes a large-diameter cylindricalpart 96 a that holds the outer circumferential portion of the bearing95, a flange part 96 b which is formed so as to extend radially outwardat a lower end portion of the large-diameter cylindrical part 96 a, anda small-diameter cylindrical part 96 c which is formed at an upper sideof the large-diameter cylindrical part 96 a.

The bearing 95 is blocked to move downward with respect to the shaftportion 93 b by a stage part provided in the shaft portion 93 b.Therefore, the spring receiving member 96 does not move downward withrespect to the shaft portion 93 b.

Further, a spring pressing member 92 c is attached to an upper portionof the external cylindrical member 92 a. In detail, a male screw partformed on the outer circumference of the spring pressing member 92 c isscrewed into a female spring part formed in the inner circumference atthe upper portion of the external cylindrical member 92 a. A main bodyof the screw tightening driver D is constituted by the gear box 91, theexternal cylindrical member 92 a, and the spring pressing member 92 c.

Then, a bit presser spring 99 is disposed between the inner ceilingplane of the spring pressing member 92 c and the flange part 96 b of thespring receiving member 96. This bit presser spring 99 biases the outputshaft 93 and the bit B downward via the spring receiving member 96, andis compressed to be deformed when the output shaft 93 moves upward alongwith the bit B.

Moreover, a conductive brush 97 enlarged to be shown on the right sideof FIG. 19 and FIG. 20 is attached to the upper part of the shaftportion 93 b. The conductive brush 97 is formed of a material with highelectrical conductivity such as copper, and includes a screw clamp part97 a fixed to the shaft portion 93 b with a screw 97 d, an extensionpart 97 b which is formed so as to extend laterally and downward fromthe screw clamp part 97 a, and a brush part 97 c which is formed so asto extend in a rotation direction of the shaft portion 93 b (in theright direction in the drawing) at a lower end of the extension part 97d.

When the screw clamp part 97 a is fixed to the shaft portion 93 b withthe screw 97 d, the brush part 97 c contacts the outer circumferentialsurface of the small-diameter cylindrical part 96 c of the springreceiving member 96. Further, while the conductive brush 97 is rotatingalong with the shaft portion 93 b (output shaft 93), the brush part 97 cslides with respect to the spring receiving member 96 (small-diametercylindrical part 96 c). Therefore, a conducting route passing from theoutput shaft 93 through the conductive brush 97, the spring receivingmember 96, and the bit presser spring 99 to the spring pressing member92 c is formed.

The bit B is connected to the output shaft 93, and as described above,the spring pressing member 92 c is screwed to engage with the externalcylindrical member 92 a. Moreover, the external cylindrical member 92 ais attached to the gear box 91. Then, the gear box 91 is connected tothe ground G as shown in FIG. 19.

In accordance therewith, static electricity charged on the bit B in thescrew tightening is introduced to the ground G via the output shaft 93,the conductive brush 97, the spring receiving member 96, the bit presserspring 99, the spring pressing member 92 c, the external cylindricalmember 92 a, and the gear box 91. Accordingly, the static electricitycharged on the bit B can be certainly prevented from having harmfuleffects on a product such as a hard disk drive vulnerable to staticelectricity through a screw tightened by the bit B. Further, since anaxial force is not applied to the conductive member, axial deformationand deterioration in electrical conductivity according the deformationcan be certainly avoided.

In this embodiment, the conducive brush 97 is fixed to the shaft portion93 b of the output shaft 93 disposed at an inner side from the springreceiving member 96 and the bit presser spring 99 with the screw 97 d.Since the spring receiving member 96 is greater in diameter than theshaft portion 93 b of the output shaft 93, the conducive brush 97 can becaused to stably slide with respect to the spring receiving member 96during the rotation of the output shaft 93. However, the conducive brushmay be fixed to the spring receiving member, and the output shaft mayrotate to slide with respect to the conducive brush.

Further, the disposition of the conducive brush 97 at the inner sidefrom the bit presser spring 99 enables effective use of a space betweenthe bit presser spring 99 and the output shaft 93 or the springreceiving member 96. Accordingly, the conducive brush 97 can be disposedwithout increasing the size of the screw tightening driver.

Embodiment 7

In the screw tightening driver described in the above-describedEmbodiments 1, 2, and 4 to 6, the motor serving as the driving sourceand the transmission mechanism that transmits a driving force from themotor to the bit for the screw tightening are inseparably integratedwith each other.

On the other hand, usually, several types of screws are used forassembling a product such as a hard disk, and torques required fortightening those screws are mutually different. In contrast thereto, arange of the output torque (tightening torque) of the screw tighteningdriver requiring especially precise torque management, i.e., a range ofthe output torque of the motor is set to be narrow. Accordingly, whentightening the several types of screws having different requiredtightening torque levels is performed by using one screw tighteningsystem, it is necessary to replace the entire screw tightening driver inaccordance with a type of the screws.

Then, FIG. 21 illustrates the configuration of a screw tightening driverin which a motor and a transmission mechanism can be separated, andthereby the motor can be replaced with respect to the transmissionmechanism, which is Embodiment 7 of the present invention. In FIG. 21,the entire screw tightening driver is shown on the left side, and thetransmission mechanism thereof is extracted to be shown on the rightside. In the following description, the upper side in FIG. 21 isreferred to as an upper side of the screw tightening driver, and thelower side in FIG. 21 is referred to as a lower side of the screwtightening driver.

In FIG. 21, reference numerals 101 and 102 respectively denote an upperbase plate and an intermediate base plate. Plural (four in thisembodiment) shaft members 104 are disposed so as to space from oneanother between the upper base plate 101 and the intermediate base plate102, and are fixed to the upper base plate 101 and the intermediate baseplate 102 with screws. Moreover, a lower base plate 103 is disposedbelow the intermediate base plate 102 via plural (four in thisembodiment) shaft members 107 which are shorter than the shaft members104 and disposed so as to space from one another. This lower base plate103 is fixed to, for example, the horizontal plate 4 a of the supporttable 4 in the screw tightening system shown in FIG. 1 in Embodiment 1.

On the other hand, plural (three in this embodiment) shaft members 105which are shorter than the shaft members 104 and disposed so as to spacefrom one another are disposed on an upper surface of the upper baseplate 101. The shaft members 105 are fixed with screws to the upper baseplate 101 from a lower surface side thereof. The shaft members 104, 105,and 107 may be round bars or square bars. Further, the number of theshaft members is arbitrary.

A supporting structure to support the transmission mechanism which willbe described later and the motor is constituted by the upper base plate101, the intermediate base plate 102, the lower base plate 103, and theshaft members 104, 105, and 107.

Reference numerals 120A and 120B denote motors corresponding to themotor M described also in Embodiments 1, 2, and 4 to 6, which are motorsrespectively having different output torque ranges.

Reference numeral 121 denotes a mounting plate, which is attached to themotor 120A or 120B with screws or the like in advance as shown in thedrawing on the right side of FIG. 21. An opening through which an outputshaft 122 of the motor 120A or 120B passes through is formed at thecenter of the mounting plate 121. Moreover, screw clamp portions 121 ato allow the shaft members 105 to be attached with screws 106 are formedin positions corresponding to the shaft members 105 fixed on the upperbase plate 101 in the peripheral part of the mounting plate 121.Reference numeral 121 b shown in the drawing on the left side of FIG. 21denotes a screw hole for fixing the motor formed in the mounting plate121.

On the other hand, as shown in the drawing on the right side of FIG. 21,a screw hole 105 a for the screw 106 is formed in the upper portion ofthe shaft member 105.

In the mounting plate 121 for the motor 120A and the mounting plate 121for the motor 120B, although the positions and the numbers of the screwholes 121 b for fixing the motor are different in some cases, thepositions and the numbers of the screw clamp portions 121 a areidentical to each other. Namely, both mounting plates 121 have a commonattachment structure for the shaft members 105. With this attachmentstructure, even if the positions and the numbers of the screw holes 121b for fixing the motors to the mounting plates 121 are different fromeach other, the motors 120A and 120B can be easily replaced to the shaftmembers 105, i.e., the supporting structure.

Next, the transmission mechanism will be described. Reference numeral110 denotes a connecting shaft which is rotatably held with respect tothe upper base plate 101 by a bearing 112 attached to the center of theupper base plate 101.

As shown in the drawing on the right side of FIG. 21, a cylindrical partis formed in the upper portion of the connecting shaft 110, and a shafthole 110 a into which the output shaft 122 of the motor 120A or 120B(hereinafter referred to as the motor output shaft) is inserted isformed in the cylindrical part. Further, two screw holes 110 b areformed in the upper and lower positions at the peripheral wall of thecylindrical part. When the motor output shaft 122 is inserted into theshaft hole 110 a, and shaft set screws 111 screwed into the respectivescrew holes 110 b come into contact with the motor output shaft 122, theoutput shaft 122 and the connecting shaft 110 can be connected so as tobe integrally rotatable. Such a screw clamp structure for the motoroutput shaft 122 enables replacement of the motor from the transmissionmechanism.

An inner shaft 114 a of an extensible shaft 114 is connected to aportion protruding downward from the upper base plate 101 in theconnecting shaft 110 via a first universal joint 113. Thus, the innershaft 114 a and the connecting shaft 110 are integrally rotatable. Theextensible shaft 114 is disposed so as to be inclined to central axes ofthe motor output shaft 122 and the connecting shaft 110.

The extensible shaft 114 has a telescopic structure constituted by theinner shaft 114 a and an outer shaft 114 b, both shafts 114 a and 114 bbeing relatively movable axially, i.e., he the extensible shaft 114being extensible. Engaging a protrusion member 114 d formed on the innershaft 114 a with a groove portion 114 c formed so as to axially extendin a side surface of the outer shaft 114 b enables integral rotation ofthe inner shaft 114 a and the outer shaft 114 b.

A bit drive shaft 117 serving as an output shaft is connected to a lowerend of the outer shaft 114 b via a second universal joint 115. The bitdrive shaft 117 is held so as to be rotatable and axially movable bybearings 116 and 118 respectively attached to the intermediate plate 102and the lower base plate 103. The bit drive shaft 117 is held so as toextend in parallel with the central axes of the motor output shaft 122and the connecting shaft 110 at a position offset (shifted) from thosecentral axes in a direction perpendicular thereto.

Moreover, a coupling 119 is attached to a lower end of the bit driveshaft 117. The coupling 119 detachably holds the bit B.

In the transmission mechanism formed as described above, a turning force(output torque) from the motor output shaft 122 is transmitted to thebit B via the connecting shaft 110, the first universal joint 113, theextensible shaft 114, the second universal joint 115, the bit driveshaft 117, and the coupling 119. In the screw tightening, the bit B andthe bit drive shaft 117 move axially, and this movement is absorbed byan extensible motion of the extensible shaft 114 and by changes of jointangles in the universal joints 113 and 115, and thereby the rotation ofthe bit B is maintained.

The first and second universal joints 113 and 115 are designed so as toeliminate eccentric rotation and inertia thereof. Further, an allowableeccentricity between the inner shaft 114 a and the outer shaft 114 b inthe extensible shaft 114 and allowable rotary eccentricities in thebearings 112, 116, and 118 are extremely little. In accordancetherewith, a torque fluctuation generated in the transmission mechanismis suppressed.

The screw tightening driver in Embodiments 1, 2, and 4 to 6 transmits amotor rotation to the output shaft and the bit via the gears. In thiscase, as described also in Embodiment 5, a tightening torque of thedriver fluctuates due to frictional fluctuations in the gears in somecases. In contrast thereto, in this embodiment, the tightening torquefluctuation due to the frictional fluctuation of the gears is not causedbecause the transmission mechanism is formed without using a train ofgears, and torque fluctuation components due to the extensible shaft 114and the bearings 112, 116, and 118 are suppressed. Therefore, a torquefluctuation can be suppressed less than that in the case where the geartransmission mechanism is used.

Then, since the torque fluctuation generated in the transmissionmechanism is little, using the method for correcting a torque correctionvalue described in Embodiment 5 together therewith enables significantsuppression of the torque fluctuation in the entire screw tighteningdriver.

In accordance with experiments by the inventors, under the sameconditions including the output torque of the motor, a torquefluctuation suppressing effect of one to several percent depending onthe level of the output torque was obtained as compared with that in agear transmission type screw tightening driver.

Moreover, in this embodiment, the motor can be replaced from thesupporting structure and the transmission mechanism. Thereby, only themotor (motor with the mounting plate 121) 120A or 120B can beappropriately selected and mounted to the supporting structure and thetransmission mechanism fixed to the lifting mechanism (refer to FIG. 1in Embodiment 1) of the screw tightening system to perform the screwtightening. Accordingly, even when screws are tightened at differenttightening torque levels, there is no need to replace the entire screwtightening driver as in the conventional art. With this advantage, evenin a case where a motor in any size is mounted, the shape and dimensionof the screw tightening driver (the supporting structure and thetransmission mechanism) except for the motor, and further the shape anddimension of the lifting mechanism and the like in the screw tighteningsystem can be remained unchanged. Accordingly, a line design time whenthe screw tightening system is installed in a production line can bereduced, and standardization of parts required for the installation andreduction of the number of the parts can be achieved.

Further, in this embodiment, the shaft members 104, 105, and 107constituting the supporting mechanism are disposed so as to space fromone another. With this disposition, at the time of a motor replacementwork and an adjustment work for the transmission mechanism associatedtherewith, a hand or a tool can be inserted into a space SP among theshaft members shown in the drawing on the left side of FIG. 21.

This embodiment described the screw tightening driver of a motorsingularly replacement type, which has the transmission mechanism usingthe universal joints. However, even in a case in which the screwtightening driver has the transmission mechanism using the gear traindescribed in Embodiment 6 or the like, a screw tightening driver of amotor singularly replacement type can be formed.

Meanwhile, a control system different from the control system descriedin Embodiments 1 to 3 can be constituted by using the screw tighteningdriver having the replaceable motor.

FIG. 22 illustrates the schematic configuration of the control system.In FIG. 22, the illustration of the mounting plates (reference numeral121 in FIG. 21) attached to the motors in advance is omitted. Further,reference symbols denoted to the screw tightening driver (the supportingmechanism and the transmission mechanism) shown on the right side in thedrawing are the same as the reference symbols in FIG. 21.

A dedicated servo controller belongs to the inseparable motor type screwtightening driver described in Embodiments 1, 2, and 4 to 6. Therefore,when the inseparable motor type screw tightening driver is replaced inaccordance with a change of a tightening torque level, it is necessaryto replace the servo controller together therewith.

In contrast thereto, in this embodiment, as shown in FIG. 22, severaltypes of motors 120A, 120B, and 120C respectively having differentoutput torque ranges can be replaced from and mounted to one screwtightening driver (the supporting mechanism and the transmissionmechanism). In such a case, it is recommended that a servo controllerSC′ capable of controlling any one of the motors 120A, 120B, and 120C beused.

In the servo controller SC′, a motor control unit C2′ that controls avoltage or an electric current applied to the respective motors, andmemories for the motors 120A, 120B, and 120C as the correction datamemories 82 to 84 described in Embodiment 5 are installed. Further,although not shown, the interpolation control unit, the adder and thelike described in Embodiment 5 as well are installed.

With this configuration, even when one of the motors 120A, 120B, and120C is mounted to the screw tightening driver, the servo controller SC′can suppress a tightening torque fluctuation to perform the screwtightening. The selection of a correction data memory corresponding tothe motor may be performed by utilizing an identification number or thelike denoted to the motor as described in Embodiment 5.

In this way, providing the function of controlling the motors 120A,120B, and 120C to the servo controller SC′ eliminates a need to replacethe servo controller even when the motor is replaced. In other words,although plural servo controllers corresponding to plural motors (screwtightening drivers) are conventionally required, this embodiment needsonly one servo controller for the plural motors 120A, 120B, and 120C.With this configuration, the screw tightening system can be formed atlower cost than the conventional art.

Embodiment 8

FIGS. 23 and 24 respectively illustrate the configuration of a screwtightening driver that is Embodiment 8 of the present invention. Thescrew tightening driver described in the above-described Embodiments 1,2, and 4 to 7 is a so-called offset-type screw tightening driver inwhich the output shaft of the motor and the bit are offset to each otherin a direction perpendicular to their central axes. However, the screwtightening driver in this embodiment is a so-called straight-type screwtightening driver in which the output shaft of the motor and the bit aredisposed on a straight line. This straight-type screw tightening driveras well can be used as the screw tightening driver described inEmbodiments 1, 2, 4, and 5.

Further, in the driver shown in FIG. 24, a brush motor 302B is usedwhich has a brush sliding with respect to a rotating commutator. On theother hand, in the driver shown in FIG. 23, a brushless motor 302A isused. Since the basic configurations other than the motors in bothdrawings are the same, constituent components in the drivers shown inFIGS. 23 and 24 identical to one another are denoted with the samereference numerals. Further, in the following description, the upperside in FIGS. 23 and 24 is referred to as an upper side of the screwtightening driver, and the lower side in the same drawings is referredto as a lower side of the screw tightening driver.

In FIGS. 23 and 24, reference numeral 301 denotes an externalcylindrical member forming a main body of the screw tightening driver.The brushless motor 302A or the brush motor 302B is fixed to an upperend portion of the external cylindrical member 301. An output shaft(hereinafter referred to as a motor output shaft) 302 a of the motor302A or 302B passes through an opening formed in an upper surface of theexternal cylindrical member 301 to protrude toward an inner side of theexternal cylindrical member 301.

Reference numeral 311 denotes a first inner cylindrical member disposedat the inner side of the external cylindrical member 301. The firstinner cylindrical member 311 is held so as to be rotatable with respectto the external cylindrical member 301 by a bearing 310 attached to theinner circumferential portion of the external cylindrical member 301.Axial movement of the first inner cylindrical member 311 with respect tothe external cylindrical member 301 is blocked by the engagement of thefirst inner cylindrical member 311 with the bearing 310.

A rotation transmission mechanism 315 which is integrally rotatable withthe motor output shaft 302 a is disposed inside of the first innercylindrical member 311. The rotation transmission mechanism 315 includesan upper member 315 a connected to the motor output shaft 302 a and alower member 315 b connected so as to be integrally rotatable andvertically movable with respect to the upper member 315 a. The lowermember 315 b engages with a D-cut shaped portion formed in an upper endof the bit B in their rotation direction. With this engagement, rotationof the motor output shaft 302 a is transmitted to the bit B via therotation transmission mechanism 315.

A ring-shaped U-groove is formed in an upper outer circumference of thebit B. Engagement of balls 316 held at a lower portion of the firstinner cylindrical member 311 with the U-groove holds the bit B so as tobe rotatable and so as not to drop off with respect to the rotationaltransmission mechanism 315.

A second inner cylindrical member 317 is disposed at an outer side ofthe first inner cylindrical member 311. A lower end surface of thesecond inner cylindrical member 317 contacts a snap ring 313 attached toan outer circumference of a lower end of the first inner cylindricalmember 311. The second inner cylindrical member 317 is biased downwardby a coil spring 319 disposed between an upper end surface of the secondinner cylindrical member 317 and a snap ring 318 attached to an upperouter circumference of the first inner cylindrical member 311. Thesecond inner cylindrical member 317 contacts, when the driver is used,the balls 316 at an inner circumferential surface of an intermediateportion of the second inner cylindrical member 317 to inhibit the balls316 holding the bit B so as to pinch it from moving toward the outside.

On the other hand, when the second inner cylindrical member 317 is movedupward with respect to the first inner cylindrical member 311 againstthe biasing force of the coil spring 319, a lower portion with a largerinner diameter in the second inner cylindrical member 317 allows theballs 316 to escape toward the outside. With this structure, the bit Bcan be detached from or attached to the driver.

A coarse adjustment male screw 301 a serving as a main body screw partis formed in a lower outer circumference of the outer cylindrical member301. With the coarse adjustment male screw 301 a, in order from theupper side, a female screw 320 a formed in an inner circumference of afirst lock ring 320 and a first female screw 321 a formed in an upperinner circumference of a coarse adjustment ring 321 serving as a firstadjustment member are respectively engaged. A coarse adjustment scale(not shown) used at the time of positioning between a lower tip end ofthe bit B and a lower tip end of a sleeve 326 which will be describedlater is provided on an outer circumference of the coarse adjustmentring 321.

A cylindrical fine adjustment case 323 serving as a second adjustmentmember is disposed outside the second cylindrical member 317 and thecoil spring 319. A fine adjustment male screw 323 a with a screw pitchless than that of the coarse adjustment male screw 301 a is formed in anupper outer circumference of the fine adjustment case 323. With the fineadjustment male screw 323 a, a second female screw 321 b formed in alower inner circumference of the coarse adjustment ring 321 and a femalescrew 324 a formed in an inner circumference of a second lock ring 324are respectively engaged in order from the upper side.

A fine adjustment scale (not shown) used at the time of adjusting aprotruding amount of the lower tip end of the bit B from the lower tipend of the sleeve 326 which will be described later is provided on anouter circumference of the fine adjustment case 323.

The sleeve 326 which covers the circumference of the lower tip end(leading end) of the bit B is disposed at a lower inner side of the fineadjustment case 323. The sleeve 326 allows the leading end of the bit Bto be exposed through its lower end opening. A flange part 326 a formedin an upper outer circumference of the sleeve 326 contacts a stageportion 323 c formed in a lower inner circumference of the fineadjustment case 323 to prevent the sleeve 326 from dropping off downwardfrom the fine adjustment case 323.

Further, the sleeve 326 is biased downward by a sleeve presser coilspring 327 engaging with an upper end surface of the sleeve 326 and anupper end portion of the fine adjustment case 323. Therefore, the sleeve326 moves up and down along with the fine adjustment case 323 at thetime of adjusting the protruding amount of the leading end of the bit Bfrom the lower tip end of the sleeve 326, the adjustment thereof beingdescribed later.

A through-hole 323 b is formed in a vertically intermediate portion on aperipheral wall portion of the fine adjustment case 323. Then, anegative pressure connection member 325 having a hole connected to thethrough-hole 323 b is attached to the outer circumference of the fineadjustment case 323.

In FIG. 24, reference numeral 302 b denotes a brush of the brush motor302B. The brush 302 b contacts the motor output shaft 302 a serving as acommutator. Reference numeral 340 denotes a cover that covers the brushmotor 302B which prevents dirt such as carbon discharged from the brushmotor 302B from going out to the outside.

An outer diameter of the screw tightening driver using the brushlessmotor 302A shown in FIG. 23 can be smaller than that of the screwtightening driver using the brush motor 302B shown in FIG. 24 becausethe brushless motor 302A does not have the cover 340. In detail, in FIG.23, the outer diameter of the brushless motor 302A and the outerdiameter of the outer cylindrical member 301 are substantially the same.Although a difference between the outer diameters of the screwtightening driver using the brushless motor 302A and the screwtightening driver using the brush motor 302B is not so large, thedifference significantly increases the volume of the entire screwtightening driver using the brush motor 302B. Accordingly, the driverusing the brushless motor 302A is advantageous to a case where pluralscrews disposed with a finer pitch are collectively tightened by pluraldrivers.

When the screw 350 is tightened by the screw tightening driver formed asdescribed above, the leading end of the bit B slightly protruded fromthe lower tip end of the sleeve 326 a is caused to engage with a recess351 of the screw 350 first, and then the lower tip end of the sleeve 326is caused to contact the upper surface of the screw 350. Then, air inthe driver is absorbed by a vacuum pump via the negative pressureconnection member 325. With this operation, the inside of the drivercomes into a negative pressure state, and the screw 350 is absorbed ontothe lower tip end of the sleeve 326. Setting the screw 350 into thescrew hole of a workpiece 352 in this state and then rotating the motor302A or 302B can tighten the screw 350.

However, since a depth DPT of the recess 351 is made shallower as thescrew 350 is miniaturized, unless the protruding amount BP of theleading end of the bit B from the lower tip end of the sleeve 326(hereinafter simply referred to as the bit protruding amount) isaccurately (strictly) adjusted, the bit protruding amount BP is toolarge, resulting in a gap between the upper surface of the screw 350 andthe lower tip end of the sleeve 326 and thereby making it impossible toabsorb the screw 350. Therefore, in the driver in this embodiment, thebit protruding amount can be accurately adjusted by the followingprocedure.

First, on the coarse adjustment male screw 301 a formed in the externalcylindrical member 301, the first lock ring 320 is loosened (movedupward) with respect to the coarse adjustment ring 321. Further, on thefine adjustment male screw 323 a formed in the fine adjustment case 323,the second lock ring 324 is loosened (moved downward) with respect tothe coarse adjustment ring 321. With these operations, the coarseadjustment ring 321 is made rotatable on the coarse adjustment malescrew 301 a.

When the coarse adjustment ring 321 is operated to be rotated in thisstate, the coarse adjustment ring 321 moves up and down with respect tothe external cylindrical member 301 by an effect of the first femalescrew 321 a of the coarse adjustment ring 321 and the coarse adjustmentmale screw 301 a of the external cylindrical member 301. At this time,the fine adjustment case 323 in which the fine adjustment male screw 323a engages with the second female screw 321 b of the coarse adjustmentring 321 and the second lock ring 324 engaging with the fine adjustmentmale screw 323 a of the fine adjustment case 323 also vertically movewith their rotation together with the coarse adjustment ring 321. Then,the sleeve 326 as well moves up and down together with the fineadjustment case 323. With this operation, the lower tip end of thesleeve 326 and the leading end of the bit B are coincided with eachother. The degree of coincidence can be secured by operating them whileviewing the scale on the coarse adjustment ring 321.

After the coincidence of the lower tip end of the sleeve 326 and theleading end of the bit B, the first lock ring 320 is tightened withrespect to the coarse adjustment ring 321. With this operation, rotationof the coarse adjustment ring 321 is prevented on the coarse adjustmentmale screw 301 a.

Next, when the fine adjustment case 323 is operated to be rotated, thefine adjustment case 323 moves up and down by an effect of the fineadjustment male screw 323 a and the second female screw 321 b of thecoarse adjustment ring 321 whose movement is locked. Then, the sleeve326 as well moves up and down together with the fine adjustment case323. As described above, since a screw pitch (i.e., a lead) of the fineadjustment male screw 323 a is less than that of the coarse adjustmentmale screw 301 a of the external cylindrical member 301, in a case wherethe rotational operating amounts are the same, a vertical movementamount of the sleeve 326 by an operation of the fine adjustment case 323is less than a vertical movement amount of the sleeve 326 by anoperation of the coarse adjustment ring 321. Accordingly, a rotationaloperation of the fine adjustment case 323 while checking the fineadjustment scale on the fine adjustment case 323 enables an extremelyprecise adjustment of the bit protruding amount BP in accordance withthe depth DPT of the recess 351 of the screw 350.

Then, at the last, the second lock ring 324 is tightened with respect tothe coarse adjustment ring 321. With this operation, rotation of thefine adjustment case 323 as well is prevented, and thereby the positionof the sleeve 326 with respect to the bit B is fixed. Namely, the bitprotruding amount BP is set.

In the conventional driver, a protruding amount of the leading end ofthe bit from the lower tip end of the sleeve is adjusted by only amember corresponding to the coarse adjustment ring 321. However, since avariation in protruding amount according to a rotational amount of themember corresponding to the coarse adjustment ring 321 is large, a fineadjustment is difficult or takes a long time. Further, there is apossibility that, when a member corresponding to the first lock ring 324is tightened, the member corresponding to the coarse adjustment ring 321as well slightly rotates by friction with the end surface of the membercorresponding to the first lock ring 324, which changes an adjustedprotruding amount. According to this embodiment, a fine adjustment forthe bit protruding amount can be easily performed in a short time.Additionally, the final locking of the fine adjustment case 323 isperformed by causing the second lock ring 324 to contact the end surfaceof the coarse adjustment ring 321 which is a separate member therefrom,thereby mostly eliminating the possibility that the bit protrudingamount is changed after the fine adjustment is completed.

The adjustment mechanism for the bit protruding amount described in thisembodiment can be employed for not only a straight-type screw tighteningdriver, but also the offset-type screw tightening driver described inEmbodiments 1, 2, and 4 to 7. Further, the mechanism enabling a coarseadjustment and a fine adjustment for a bit protruding amount is notlimited to that having the above-described configuration.

Furthermore, the present invention is not limited to these embodimentsand various variations and modifications may be made without departingfrom the scope of the present invention.

1. A screw tightening apparatus comprising: a motor; an output shaft towhich a bit for screw tightening is connected so as to be rotatableintegrally with the output shaft and which is axially movable, theoutput shaft being driven to be rotated by the motor; a spring whose oneend contacts a member constituting a main body of the screw tighteningapparatus; a spring receiving member which the other end of the springcontacts, the spring receiving member transmitting a biasing force ofthe spring to the output shaft; and a conductive member which contactsthe output shaft and the spring receiving member.
 2. The screwtightening apparatus according to claim 1, wherein the conductive memberis attached to the output shaft to slide with respect to the springreceiving member in a state in which the output shaft is rotating. 3.The screw tightening apparatus according to claim 1, wherein theconductive member contacts the output shaft and the spring receivingmember at an inner side of the spring.